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VLT (Very Large Telescope) of ESO on Cerro Paranal

Mission Status    VLT development and instruments    ESPRESSO    Hawk-I    FLAMES    MATISSE    GRAVITY    MUSE    References

VLT is a telescope facility operated by ESO (European Southern Observatory) on the Cerro Paranal mountain in the Atacama Desert of northern Chile at an elevation of 2,635 m (coordinates: 24°37'38''S, 70°24'17''W).

VLT is the flagship facility for European ground-based astronomy at the beginning of the third Millennium. It is the world's most advanced optical instrument, consisting of four Unit Telescopes with main mirrors of 8.2m diameter and four movable 1.8m diameter ATs (Auxiliary Telescopes). The telescopes can work together, to form a giant ‘interferometer’, the ESO VLTI (Very Large Telescope Interferometer), allowing astronomers to see details up to 25 times finer than with the individual telescopes. The VLTI functions like a telescope with a mirror 200 m in diameter. The light beams are combined in the VLTI using a complex system of mirrors in underground tunnels where the light paths must be kept equal to distances less than 1/1000 mm over a hundred meters. With this kind of precision, the VLTI can reconstruct images with an angular resolution of milliarcseconds (marcsec), equivalent to distinguishing the two headlights of a car at the distance of the Moon. 1)

ESO is the foremost intergovernmental astronomy organization in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and by Australia as a strategic partner. ESO carries out an ambitious program focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organizing cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: , Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA (Visible and Infrared Survey Telescope for Astronomy) works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-meter ELT (Extremely Large Telescope), which will become “the world’s biggest eye on the sky”.

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Figure 1: Aerial view of the observing platform on the top of Cerro Paranal, with the four enclosures for the 8.2-m UTs (Unit Telescopes) and various installations for the VLT Interferometer (VLTI). Three 1.8 m VLTI ATs (Auxiliary Telescopes) and paths of the light beams have been superimposed on the photo. Also seen are some of the 30 "stations" where the ATs will be positioned for observations and from where the light beams from the telescopes can enter the Interferometric Tunnel below. The straight structures are supports for the rails on which the telescopes can move from one station to another. The Interferometric Laboratory (partly subterranean) is at the center of the platform (image credit: ESO)

The 8.2m diameter Unit Telescopes can also be used individually. With one such telescope, images of celestial objects as faint as magnitude 30 can be obtained in a one-hour exposure. This corresponds to seeing objects that are four billion (four thousand million) times fainter than what can be seen with the unaided eye.

The large telescopes are named Antu, Kueyen, Melipal and Yepun, which are the names for the Sun, the Moon, the Southern Cross, and Venus in the language of the Mapuche people.

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Figure 2: Alternate view of ESO's Paranal Observatory hosting several world-class telescopes; among them are the Very Large Telescope, the Visible and Infrared Survey Telescope for Astronomy, and the VLT Survey Telescope. Other scientific and support facilities are also located at Paranal, including several smaller telescopes and an innovative accommodation facility known as the Residencia (image credit: ESO) 2)


Some Background:

ESO (European Southern Observatory) is a 16-nation intergovernmental research organization for ground-based astronomy. Created in 1962, ESO has provided astronomers with state-of-the-art research facilities and access to the southern sky. The organization employs about 730 staff members and receives annual member state contributions of approximately €131 million. Its observatories are located in northern Chile. 3)

ESO has built and operated some of the largest and most technologically advanced telescopes. These include the NTT (New Technology Telescope), an early pioneer in the use of active optics, and the VLT (Very Large Telescope), which consists of four individual telescopes, each with a primary mirror 8.2 m across, and four smaller auxiliary telescopes. The ALMA (Atacama Large Millimeter Array) observes the universe in the millimeter and su-millimeter wavelength ranges, and is the world's largest ground-based astronomy project to date. It was completed in March 2013 in an international collaboration by Europe (represented by ESO), North America, East Asia and Chile.

Currently under construction is the ELT (Extremely Large Telescope). It will use a 39.3 meter diameter segmented mirror, and become the world's largest optical reflecting telescope when operational in 2024. Its light-gathering power will allow detailed studies of planets around other stars, the first objects in the universe, supermassive black holes, and the nature and distribution of the dark matter and dark energy which dominate the universe.

ESO's observing facilities have made astronomical discoveries and produced several astronomical catalogs. Its findings include the discovery of the most distant gamma-ray burst and evidence for a black hole at the center of the Milky Way.

In 2004, the VLT allowed astronomers to obtain the first picture of an extrasolar planet (2M1207b) orbiting a brown dwarf 173 light-years away. The HARPS (High Accuracy Radial Velocity Planet Searcher) instrument installed in another ESO telescope led to the discovery of extrasolar planets, including Gliese 581c—one of the smallest planets seen outside the solar system.

Construction of the VLT began in 1991, and its first observations were made in 1998. Among the VLT’s notable discoveries are the first direct spectrum of an extrasolar planet, HR 8799c, and the first direct measurement of the mass of an extrasolar planet, HD 209458b. The VLT also discovered the most massive star known, R136a1, which has a mass 265 times that of the Sun. The VLT is operated by the European Southern Observatory. 4)

Chilean observation sites:

Although ESO is headquartered in Garching, Germany, its telescopes and observatories are in northern Chile, where the organization operates advanced ground-based astronomical facilities:

La Silla, which hosts the New Technology Telescope (NTT)

Paranal, where the VLT (Very Large Telescope) is located

Llano de Chajnantor, which hosts the APEX (Atacama Pathfinder Experiment) submillimeter telescope and where ALMA (Atacama Large Millimeter/submillimeter Array), is located.

These are among the best locations for astronomical observations in the southern hemisphere. An ESO project is the ELT (Extremely Large Telescope), a 40 m class telescope based on a five-mirror design and the formerly planned Overwhelmingly Large Telescope. The ELT will be the largest optical near-infrared telescope in the world. ESO began its design in early 2006, and aimed to begin construction in 2012. Construction work at the ELT site started in June 2014. As decided by the ESO council on 26 April 2010, a fourth site (Cerro Armazones) is to be home to ELT.

Each year about 2,000 requests are made for the use of ESO telescopes, for four to six times more nights than are available. Observations made with these instruments appear in a number of peer-reviewed publications annually; in 2009, more than 650 reviewed papers based on ESO data were published.

ESO telescopes generate large amounts of data at a high rate, which are stored in a permanent archive facility at ESO headquarters. The archive contains more than 1.5 million images (or spectra) with a total volume of about 65 TB of data.

Name

Acronym

Size

Type

Location (Chile)

Year

ESO 3.6 m telescope – hosting HARPS

ESO 3.6 m

3.57 m

optical and infrared

La Silla

1977

MPG/ESO 2.2 m telescope

MPG

2.20 m

optical and infrared

La Silla

1984

New Technology Telescope

NTT

3.58 m

optical and infrared

La Silla

1989

Very Large Telescope

VLT

4 x 8.2 m, 4 x 1.8 m

optical and mid-infrared

Paranal

1998

Atacama Pathfinder Experiment

APEX

12 m

mm/sub-mm wavelength

Chajnantor

2005

Visible and Infrared Survey Telescope for Astronomy

VISTA

4.1 m

near-infrared, survey

Paranal

2009

VLT Survey Telescope

VST

2.6 m

optical, survey

Paranal

2011

Atacama Large Millimeter/submillimeter Array

ALMA

50 x 12 m, 12 x 7 m
4 x 12 m

mm/sub-mm interferometer
array

Chajnantor

2011

Extremely Large Telescope

ELT

39.3 m

optical to mid-infrared

Cerro Amazones

2024

Table 1: ESO telescopes

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Figure 3: Aerial view of Paranal with VISTA in the foreground and the VLT (Very Large Telescope) in the background (image credit: ESO/G.Hüdepohl)




Sample Observations with VLT (Very Large Telescope) and some status

• September 3, 2020: A team of astronomers have identified the first direct evidence that groups of stars can tear apart their planet-forming disc, leaving it warped and with tilted rings. This new research suggests exotic planets, not unlike Tatooine in Star Wars, may form in inclined rings in bent discs around multiple stars. The results were made possible thanks to observations with the European Southern Observatory’s Very Large Telescope (ESO’s VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA). 5)

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Figure 4: ALMA and the Sphere instrument on the VLT have imaged GW Orionis, a triple star system with a peculiar inner region. The new observations revealed that this object has a warped planet-forming disc with a misaligned ring. In particular, the SPHERE image (right panel) allowed astronomers to see, for the first time, the shadow that this ring casts on the rest of the disc. This helped them figure out the 3D shape of the ring and the overall disc. The left panel shows an artistic impression of the inner region of the disc, including the ring, which is based on the 3D shape reconstructed by the team (image credit: ESO, L. Calçada, Exeter/Kraus, et al.)

- Our Solar System is remarkably flat, with the planets all orbiting in the same plane. But this is not always the case, especially for planet-forming discs around multiple stars, like the object of the new study: GW Orionis. This system, located just over 1300 light-years away in the constellation of Orion, has three stars and a deformed, broken-apart disc surrounding them.

- “Our images reveal an extreme case where the disc is not flat at all, but is warped and has a misaligned ring that has broken away from the disc,” says Stefan Kraus, a professor of astrophysics at the University of Exeter in the UK who led the research published today in the journal Science. The misaligned ring is located in the inner part of the disc, close to the three stars. 6)

- The new research also reveals that this inner ring contains 30 Earth-masses of dust, which could be enough to form planets. “Any planets formed within the misaligned ring will orbit the star on highly oblique orbits and we predict that many planets on oblique, wide-separation orbits will be discovered in future planet imaging campaigns, for instance with the ELT,” says team member Alexander Kreplin of the University of Exeter, referring to ESO’s Extremely Large Telescope, which is planned to start operating later this decade. Since more than half the stars in the sky are born with one or more companions, this raises an exciting prospect: there could be an unknown population of exoplanets that orbit their stars on very inclined and distant orbits.

- To reach these conclusions, the team observed GW Orionis for over 11 years. Starting in 2008, they used the AMBER and later the GRAVITY instruments on ESO’s VLT Interferometer in Chile, which combines the light from different VLT telescopes, to study the gravitational dance of the three stars in the system and map their orbits. “We found that the three stars do not orbit in the same plane, but their orbits are misaligned with respect to each other and with respect to the disc,” says Alison Young of the Universities of Exeter and Leicester and a member of the team.

- They also observed the system with the SPHERE instrument on ESO’s VLT and with ALMA, in which ESO is a partner, and were able to image the inner ring and confirm its misalignment. ESO’s SPHERE also allowed them to see, for the first time, the shadow that this ring casts on the rest of the disc. This helped them figure out the 3D shape of the ring and the overall disc.

- The international team, which includes researchers from the UK, Belgium, Chile, France and the US, then combined their exhaustive observations with computer simulations to understand what had happened to the system. For the first time, they were able to clearly link the observed misalignments to the theoretical “disc-tearing effect”, which suggests that the conflicting gravitational pull of stars in different planes can warp and break their discs.

- Their simulations showed that the misalignment in the orbits of the three stars could cause the disc around them to break into distinct rings, which is exactly what they see in their observations. The observed shape of the inner ring also matches predictions from numerical simulations on how the disc would tear.

- Interestingly, another team who studied the same system using ALMA believe another ingredient is needed to understand the system. “We think that the presence of a planet between these rings is needed to explain why the disc tore apart,” says Jiaqing Bi of the University of Victoria in Canada who led a study of GW Orionis published in The Astrophysical Journal Letters in May this year. His team identified three dust rings in the ALMA observations, with the outermost ring being the largest ever observed in planet-forming discs.

- Future observations with ESO’s ELT and other telescopes may help astronomers fully unravel the nature of GW Orionis and reveal young planets forming around its three stars.

• August 28, 2020: A team including researchers from the Institute for Astrophysics of the University of Cologne has for the first time directly observed the columns of matter that build up newborn stars. This was observed in the young star TW Hydrae system located approximately 163 light years from Earth. This result was obtained with the VLTI (Very Large Telescope Interferometer) and its GRAVITY instrument of the European Southern Observatory (ESO) in Chile. The article 'A measure of the size of the magnetospheric accretion region in TW Hydrae' has been published in a recent issue of Nature. 7) 8)

- The formation of stars in the Galaxy involves processes in which primordial matter such as gas and dust present in the giant molecular clouds is rapidly aggregated via gravity to form a protostar. This 'accretion' of gas occurs through the disk that forms around the newborn star and represents the major mechanism of supply of material to the growing central baby star. These so-called protoplanetary disks are one of the key ingredients to explain the formation of very diverse exoplanets that are to date frequently discovered orbiting our closest neighbors.

- Based on theoretical and observational evidence, many scenarios were hypothesized to describe the mechanism of interaction between the star and the parent circumstellar disk, like for instance the funnelling and accretion of host gas onto the central star along the local magnetic field. But this could never be directly observed and proven so far with any telescope. The main reason is that the level of details of the image - astronomers talk about angular resolution - necessary to observe what happens very close to the star was simply out of reach. For comparison, detecting these events would be like discerning a small one-cubic meter box on the surface of the Moon. With a normal telescope, this is not possible. However, with an interferometer like the VLTI in Chile and its instrument GRAVITY, which delivers unprecedented angular resolution in the infrared, such a precise observation has now become possible. An interferometer collects and combines the light from different telescopes a few hundred meters apart, which provides the same level of accuracy as a hypothetical giant telescope with a comparable diameter.

- With the contribution of members of Cologne's Institute for Astrophysics, astrophysicists from several European institutions exploited the GRAVITY instrument at the VLTI to probe the closest regions around the young solar analog TW Hydrae, which is thought to be the most representative example of what our Sun may have looked like at the time of its formation, more than 5 billion years ago. By measuring very precisely the typical angular size of the very inner gaseous regions - using a particular infrared atomic transition of the hot hydrogen gas - the scientists were able to directly prove that the hot gas emission was indeed resulting from magnetospheric accretion taking place very close to the stellar surface. 'This is an important milestone in our attempt to confirm the mechanisms at work in the field of star formation', said Professor Lucas Labadie, co-author of the paper. 'We now want to extend such exploration to other young stars of different nature to understand how the evolution of the circumstellar disk, the birthplace of planets, goes.'

- The team is part of the GRAVITY collaboration, named after the instrument that was co-developed by the University of Cologne and which combines interferometrically the four large VLT 8-m telescopes of ESO in Chile. The team members include Lucas Labadie, Rebekka Grellmann, Andreas Eckart, Matthew Horrobin, Christian Straubmeier and Michael Wiest. 'This result illustrates what is the unique potential of interferometry at the VLTI', added Dr Christian Straubmeier, team member and co-investigator of the GRAVITY instrument in Cologne. 'This is why we decided to look ahead and develop the upgrade GRAVITY+ in the hope of being able to observe and image even fainter objects than what GRAVITY currently does.'

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Figure 5: Artist's Impression of the Streams of Hot Gas that Build up Stars. Matter from the surrounding protoplanetary disk, the birthplace of planets, is channeled onto the stellar surface by magnetic fields shocking the surface at supersonic velocity (image credit: University of Cologne, Mark A. Garlick)

• July 30, 2020: Resembling a butterfly with its symmetrical structure, beautiful colors, and intricate patterns, this striking bubble of gas — known as NGC 2899 — appears to float and flutter across the sky in this new picture from ESO’s Very Large Telescope (VLT). This object has never before been imaged in such striking detail, with even the faint outer edges of the planetary nebula glowing over the background stars. 9)

- NGC 2899’s vast swathes of gas extend up to a maximum of two light-years from its center, glowing brightly in front of the stars of the Milky Way as the gas reaches temperatures upwards of ten thousand degrees. The high temperatures are due to the large amount of radiation from the nebula’s parent star, which causes the hydrogen gas in the nebula to glow in a reddish halo around the oxygen gas, in blue.

- This object, located between 3000 and 6500 light-years away in the Southern constellation of Vela (The Sails), has two central stars, which are believed to give it its nearly symmetric appearance. After one star reached the end of its life and cast off its outer layers, the other star now interferes with the flow of gas, forming the two-lobed shape seen here. Only about 10–20% of planetary nebulae [1] display this type of bipolar shape.

- Astronomers were able to capture this highly detailed image of NGC 2899 using the FORS (FOcal Reducer and low dispersion Spectrograph) instrument installed on UT1 (Antu), one of the four 8.2-meter telescopes that make up ESO’s VLT in Chile. Standing for FOcal Reducer and low dispersion Spectrograph, this high-resolution instrument was one of the first to be installed on ESO’s VLT and is behind numerous beautiful images and discoveries from ESO. FORS has contributed to observations of light from a gravitational wave source, has researched the first known interstellar asteroid, and has been used to study in depth the physics behind the formation of complex planetary nebulae.

- This image (Figure 6) was created under the ESO Cosmic Gems program, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The program makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

- Notes: [1] Unlike what their common name suggests, planetary nebulae have nothing to do with planets. The first astronomers to observe them merely described them as planet-like in appearance. They are instead formed when ancient stars with up to 6 times the mass of our Sun reach the end of their lives, collapse, and blow off expanding shells of gas, rich in heavy elements. Intense ultraviolet radiation energizes and lights up these moving shells, causing them to shine brightly for thousands of years until they ultimately disperse slowly through space, making planetary nebulae relatively short-lived phenomena on astronomical timescales.

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Figure 6: This highly detailed image of the fantastic NGC 2899 planetary nebula was captured using the FORS instrument on ESO’s VLT (Very Large Telescope) in northern Chile. This object has never before been imaged in such striking detail, with even the faint outer edges of the planetary nebula glowing over the background stars (image credit: ESO)

• July 22, 2020: ESO's VLT has taken the first-ever image of a young, Sun-like star accompanied by two giant exoplanets. Images of systems with multiple exoplanets are extremely rare, and — until now — astronomers had never directly observed more than one planet orbiting a star similar to the Sun. The observations can help astronomers understand how planets formed and evolved around our own Sun. 10) 11)

- Just a few weeks ago, ESO revealed a planetary system being born in a new, stunning VLT image. Now, the same telescope, using the same instrument, has taken the first direct image of a planetary system around a star like our Sun, located about 300 light-years away and known as TYC 8998-760-1.

- “This discovery is a snapshot of an environment that is very similar to our Solar System, but at a much earlier stage of its evolution,” says Alexander Bohn, a PhD student at Leiden University in the Netherlands, who led the new research published today in The Astrophysical Journal Letters. 12)

- “Even though astronomers have indirectly detected thousands of planets in our galaxy, only a tiny fraction of these exoplanets have been directly imaged,” says co-author Matthew Kenworthy, Associate Professor at Leiden University, adding that “direct observations are important in the search for environments that can support life.” The direct imaging of two or more exoplanets around the same star is even more rare; only two such systems have been directly observed so far, both around stars markedly different from our Sun. The new ESO’s VLT image is the first direct image of more than one exoplanet around a Sun-like star. ESO’s VLT was also the first telescope to directly image an exoplanet, back in 2004, when it captured a speck of light around a brown dwarf, a type of ‘failed’ star.

- “Our team has now been able to take the first image of two gas giant companions that are orbiting a young, solar analogue,” says Maddalena Reggiani, a postdoctoral researcher from KU Leuven, Belgium, who also participated in the study. The two planets can be seen in the new image as two bright points of light distant from their parent star, which is located in the upper left of the frame (click on the image to view the full frame). By taking different images at different times, the team were able to distinguish these planets from the background stars.

- The two gas giants orbit their host star at distances of 160 and about 320 times the Earth-Sun distance. This places these planets much further away from their star than Jupiter or Saturn, also two gas giants, are from the Sun; they lie at only 5 and 10 times the Earth-Sun distance, respectively. The team also found the two exoplanets are much heavier than the ones in our Solar System, the inner planet having 14 times Jupiter’s mass and the outer one six times.

- Bohn’s team imaged this system during their search for young, giant planets around stars like our Sun but far younger. The star TYC 8998-760-1 is just 17 million years old and located in the Southern constellation of Musca (The Fly). Bohn describes it as a “very young version of our own Sun.”

- These images were possible thanks to the high performance of the SPHERE instrument on ESO’s VLT in the Chilean Atacama desert. SPHERE blocks the bright light from the star using a device called coronagraph, allowing the much fainter planets to be seen. While older planets, such as those in our Solar System, are too cool to be found with this technique, young planets are hotter, and so glow brighter in infrared light. By taking several images over the past year, as well as using older data going back to 2017, the research team have confirmed that the two planets are part of the star’s system.

- Further observations of this system, including with the future ESO Extremely Large Telescope (ELT), will enable astronomers to test whether these planets formed at their current location distant from the star or migrated from elsewhere. ESO’s ELT will also help probe the interaction between two young planets in the same system. Bohn concludes: “The possibility that future instruments, such as those available on the ELT, will be able to detect even lower-mass planets around this star marks an important milestone in understanding multi-planet systems, with potential implications for the history of our own Solar System.”

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Figure 7: This image, captured by the SPHERE instrument on ESO’s Very Large Telescope, shows the star TYC 8998-760-1 accompanied by two giant exoplanets, TYC 8998-760-1b and TYC 8998-760-1c. This is the first time astronomers have directly observed more than one planet orbiting a star similar to the Sun. The two planets are visible as two bright dots in the center (TYC 8998-760-1b) and bottom right (TYC 8998-760-1c) of the frame. Other bright dots, which are background stars, are visible in the image as well. By taking different images at different times, the team were able to distinguish these planets from the background stars. The image was captured by blocking the light from the young, Sun-like star (top-left of center) using a coronagraph, which allows for the fainter planets to be detected. The bright and dark rings we see on the star’s image are optical artefacts (image credit: ESO/Bohn et al.)

• June 30, 2020: Using the European Southern Observatory’s Very Large Telescope (VLT), astronomers have discovered the absence of an unstable massive star in a dwarf galaxy. Scientists think this could indicate that the star became less bright and partially obscured by dust. An alternative explanation is that the star collapsed into a black hole without producing a supernova. “If true,” says team leader and PhD student Andrew Allan of Trinity College Dublin, Ireland, “this would be the first direct detection of such a monster star ending its life in this manner.” 13)

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Figure 8: Artist’s impression of the disappearing star. This illustration shows what the luminous blue variable star in the Kinman Dwarf galaxy could have looked like before its mysterious disappearance (image credit: ESO/L. Calçada)

- Between 2001 and 2011, various teams of astronomers studied the mysterious massive star, located in the Kinman Dwarf galaxy, and their observations indicated it was in a late stage of its evolution. Allan and his collaborators in Ireland, Chile and the US wanted to find out more about how very massive stars end their lives, and the object in the Kinman Dwarf seemed like the perfect target. But when they pointed ESO’s VLT to the distant galaxy in 2019, they could no longer find the telltale signatures of the star. “Instead, we were surprised to find out that the star had disappeared!” says Allan, who led a study of the star published today in Monthly Notices of the Royal Astronomical Society. 14)

- Located some 75 million light-years away in the constellation of Aquarius, the Kinman Dwarf galaxy is too far away for astronomers to see its individual stars, but they can detect the signatures of some of them. From 2001 to 2011, the light from the galaxy consistently showed evidence that it hosted a ‘luminous blue variable’ star some 2.5 million times brighter than the Sun. Stars of this type are unstable, showing occasional dramatic shifts in their spectra and brightness. Even with those shifts, luminous blue variables leave specific traces scientists can identify, but they were absent from the data the team collected in 2019, leaving them to wonder what had happened to the star. “It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion,” says Allan.

- The group first turned the ESPRESSO instrument toward the star in August 2019, using the VLT’s four 8-meter telescopes simultaneously. But they were unable to find the signs that previously pointed to the presence of the luminous star. A few months later, the group tried the X-shooter instrument, also on ESO’s VLT, and again found no traces of the star.

- “We may have detected one of the most massive stars of the local Universe going gently into the night,” says team-member Jose Groh, also of Trinity College Dublin. “Our discovery would not have been made without using the powerful ESO 8-meter telescopes, their unique instrumentation, and the prompt access to those capabilities following the recent agreement of Ireland to join ESO.” Ireland became an ESO member state in September 2018.

- The team then turned to older data collected using X-shooter and the UVES instrument on ESO’s VLT, located in the Chilean Atacama Desert, and telescopes elsewhere.“The ESO Science Archive Facility enabled us to find and use data of the same object obtained in 2002 and 2009,” says Andrea Mehner, a staff astronomer at ESO in Chile who participated in the study. “The comparison of the 2002 high-resolution UVES spectra with our observations obtained in 2019 with ESO's newest high-resolution spectrograph ESPRESSO was especially revealing, from both an astronomical and an instrumentation point of view.”

- The old data indicated that the star in the Kinman Dwarf could have been undergoing a strong outburst period that likely ended sometime after 2011. Luminous blue variable stars such as this one are prone to experiencing giant outbursts over the course of their life, causing the stars’ rate of mass loss to spike and their luminosity to increase dramatically.

- Based on their observations and models, the astronomers have suggested two explanations for the star’s disappearance and lack of a supernova, related to this possible outburst. The outburst may have resulted in the luminous blue variable being transformed into a less luminous star, which could also be partly hidden by dust. Alternatively, the team says the star may have collapsed into a black hole, without producing a supernova explosion. This would be a rare event: our current understanding of how massive stars die points to most of them ending their lives in a supernova.

- Future studies are needed to confirm what fate befell this star. Planned to begin operations in 2025, ESO’s Extremely Large Telescope (ELT) will be capable of resolving stars in distant galaxies such as the Kinman Dwarf, helping to solve cosmic mysteries such as this one.

• May 28, 2020: Researchers from the University of Geneva, have confirmed the existence of the Proxima b extrasolar planet using measurements from the Swiss-built ESPRESSO spectrograph on ESO's VLT (Very Large Telescope) in Chile. 15)

- The existence of a planet the size of Earth around the closest star in the solar system, Proxima Centauri, has been confirmed by an international team of scientists including researchers from the University of Geneva (UNIGE). The results, which you can read all about in the journal Astronomy & Astrophysics, reveal that the planet in question, Proxima b, has a mass of 1.17 earth masses and is located in the habitable zone of its star, which it orbits in 11.2 days. This breakthrough has been possible thanks to radial velocity measurements of unprecedented precision using ESPRESSO, the Swiss-manufactured spectrograph – the most accurate currently in operation – which is installed on the Very Large Telescope in Chile. Proxima b was first detected four years ago by means of an older spectrograph, HARPS – also developed by the Geneva-based team – which measured a low disturbance in the star’s speed, suggesting the presence of a companion.

- The ESPRESSO spectrograph has performed radial velocity measurements on the star Proxima Centauri, which is only 4.2 light-years from the Sun, with an accuracy of 30 cm/s or about three times more precise than that obtained with HARPS, the same type of instrument but from the previous generation.

- “We were already very happy with the performance of HARPS (High Accuracy Radial Velocity Planet Searcher), which has been responsible for discovering hundreds of exoplanets over the last 17 years”, begins Francesco Pepe, a professor in the Astronomy Department in UNIGE’s Faculty of Science and the man in charge of ESPRESSO. “We’re really pleased that ESPRESSO can produce even better measurements, and it’s gratifying and just reward for the teamwork lasting nearly 10 years.”

- Alejandro Suarez Mascareño, the article’s main author, adds: “Confirming the existence of Proxima b was an important task, and it’s one of the most interesting planets known in the solar neighborhood.”

- The measurements performed by ESPRESSO have clarified that the minimum mass of Proxima b is 1.17 earth masses (the previous estimate was 1.3) and that it orbits around its star in only 11.2 days.

- “ESPRESSO has made it possible to measure the mass of the planet with a precision of over one-tenth of the mass of Earth”, says Michel Mayor, winner of the Nobel Prize for Physics in 2019, honorary professor in the Faculty of Science and the ‘architect’ of all ESPRESSO-type instruments. “It’s completely unheard of.”

And what about life in all this?

- Although Proxima b is about 20 times closer to its star than the Earth is to the Sun, it receives comparable energy, so that its surface temperature could mean that water (if there is any) is in liquid form in places and might, therefore, harbor life.

- Having said that, although Proxima b is an ideal candidate for biomarker research, there is still a long way to go before we can suggest that life has been able to develop on its surface. In fact, the Proxima star is an active red dwarf that bombards its planet with X rays, receiving about 400 times more than the Earth.

- “Is there an atmosphere that protects the planet from these deadly rays?” asks Christophe Lovis, a researcher in UNIGE’s Astronomy Department and responsible for ESPRESSO’s scientific performance and data processing. “And if this atmosphere exists, does it contain the chemical elements that promote the development of life (oxygen, for example)? How long have these favorable conditions existed? We’re going to tackle all these questions, especially with the help of future instruments like the RISTRETTO spectrometer, which we’re going to build specially to detect the light emitted by Proxima b, and HIRES, which will be installed on the future ELT 39 m giant telescope that the European Southern Observatory (ESO) is building in Chile.”

Surprise: is there a second planet?

- In the meantime, the precision of the measurements made by ESPRESSO could result in another surprise. The team has found evidence of a second signal in the data, without being able to establish the definitive cause behind it. “If the signal was planetary in origin, this potential other planet accompanying Proxima b would have a mass less than one third of the mass of the Earth. It would then be the smallest planet ever measured using the radial velocity method”, adds Professor Pepe.

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Figure 9: This artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System (image credit: ESO, M. Kornmesser)

- It should be noted that ESPRESSO, which became operational in 2017, is in its infancy and these initial results are already opening up undreamt of opportunities. The road has been travelled at breakneck pace since the first extrasolar planet was discovered by Michel Mayor and Didier Queloz, both from UNIGE’s Astronomy Department. In 1995, the 51Peg b gas giant planet was detected using the ELODIE spectrograph with an accuracy of 10 m/s. Today ESPRESSO, with its 30 cm/s (and soon 10 after the latest adjustments) will perhaps make it possible to explore worlds that remind us of the Earth. 16)

• May 20, 2020: Observations made with the European Southern Observatory’s Very Large Telescope (ESO’s VLT) have revealed the telltale signs of a star system being born. Around the young star AB Aurigae lies a dense disc of dust and gas in which astronomers have spotted a prominent spiral structure with a ‘twist’ that marks the site where a planet may be forming. The observed feature could be the first direct evidence of a baby planet coming into existence. 17) 18)

- “Thousands of exoplanets have been identified so far, but little is known about how they form,” says Anthony Boccaletti who led the study from the Observatoire de Paris, PSL University, France. Astronomers know planets are born in dusty discs surrounding young stars, like AB Aurigae, as cold gas and dust clump together. The new observations with ESO’s VLT, published in Astronomy & Astrophysics, provide crucial clues to help scientists better understand this process.

- “We need to observe very young systems to really capture the moment when planets form,” says Boccaletti. But until now astronomers had been unable to take sufficiently sharp and deep images of these young discs to find the ‘twist’ that marks the spot where a baby planet may be coming to existence.

- The new images feature a stunning spiral of dust and gas around AB Aurigae, located 520 light-years away from Earth in the constellation of Auriga (The Charioteer). Spirals of this type signal the presence of baby planets, which ‘kick’ the gas, creating “disturbances in the disc in the form of a wave, somewhat like the wake of a boat on a lake,” explains Emmanuel Di Folco of the Astrophysics Laboratory of Bordeaux (LAB), France, who also participated in the study. As the planet rotates around the central star, this wave gets shaped into a spiral arm. The very bright yellow ‘twist’ region close to the center of the new AB Aurigae image, which lies at about the same distance from the star as Neptune from the Sun, is one of these disturbance sites where the team believe a planet is being made.

- Observations of the AB Aurigae system made a few years ago with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, provided the first hints of ongoing planet formation around the star. In the ALMA images, scientists spotted two spiral arms of gas close to the star, lying within the disc’s inner region. Then, in 2019 and early 2020, Boccaletti and a team of astronomers from France, Taiwan, the US and Belgium set out to capture a clearer picture by turning the SPHERE instrument on ESO’s VLT in Chile toward the star. The SPHERE images are the deepest images of the AB Aurigae system obtained to date.

- With SPHERE's powerful imaging system, astronomers could see the fainter light from small dust grains and emissions coming from the inner disc. They confirmed the presence of the spiral arms first detected by ALMA and also spotted another remarkable feature, a ‘twist’, that points to the presence of ongoing planet formation in the disc. "The twist is expected from some theoretical models of planet formation,” says co-author Anne Dutrey, also at LAB. “It corresponds to the connection of two spirals — one winding inwards of the planet’s orbit, the other expanding outwards — which join at the planet location. They allow gas and dust from the disc to accrete onto the forming planet and make it grow."

- ESO is constructing the 39-meter ELT (Extremely Large Telescope), which will draw on the cutting-edge work of ALMA and SPHERE to study extrasolar worlds. As Boccaletti explains, this powerful telescope will allow astronomers to get even more detailed views of planets in the making. “We should be able to see directly and more precisely how the dynamics of the gas contributes to the formation of planets,” he concludes.

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Figure 10: This image shows the disc around the young AB Aurigae star, where ESO’s Very Large Telescope (VLT) has spotted signs of planet birth. Close to the center of the image, in the inner region of the disc, we see the ‘twist’ (in very bright yellow) that scientists believe marks the spot where a planet is forming. This twist lies at about the same distance from the AB Aurigae star as Neptune from the Sun. The image was obtained with the VLT’s SPHERE instrument in polarized light (image credit: ESO/Boccaletti et al.)

• May 01, 2020: An international team of astronomers has captured fifteen images of the inner rims of planet-forming disks located hundreds of light years away. These disks of dust and gas, similar in shape to a music record, form around young stars. The images shed new light on how planetary systems are formed. They were published in the journal Astronomy and Astrophysics. 19) 20)

- To understand how planetary systems, including our own, take shape, you have to study their origins. Planet-forming or protoplanetary disks are formed in unison with the star they surround. The dust grains in the disks can grow into larger bodies, which eventually leads to the formation of planets. Rocky planets like the Earth are believed to form in the inner regions of protoplanetary disks, less than five astronomical units (five times the Earth-Sun distance) from the star around which the disk has formed.

- Before this new study, several pictures of these disks had been taken with the largest single-mirror telescopes, but these cannot capture their finest details. “In these pictures, the regions close to the star, where rocky planets form, are covered by only few pixels,” says lead author Jacques Kluska from KU Leuven in Belgium. “We needed to visualize these details to be able to identify patterns that might betray planet formation and to characterize the properties of the disks." This required a completely different observation technique. “I’m thrilled that we now for the first time have fifteen of these images,” Kluska continues.

Image reconstruction

- Kluska and his colleagues created the images at the European Southern Observatory (ESO) in Chile by using a technique called infrared interferometry. Using ESO’s PIONIER instrument, they combined the light collected by four telescopes at the VLT (Very Large Telescope) observatory to capture the disks in detail. However, this technique does not deliver an image of the observed source. The details of the disks needed to be recovered with a mathematical reconstruction technique. This technique is similar to how the first image of a black hole was captured. “We had to remove the light of the star, as it hindered the level of detail we could see in the disks,” Kluska explains.

- “Distinguishing details at the scale of the orbits of rocky planets like Earth or Jupiter (as you can see in the images) – a fraction of the Earth-Sun distance – is equivalent to being able to see a human on the Moon, or to distinguish a hair at a 10 km distance,” notes Jean-Philippe Berger of the Université Grenoble-Alpes, who as principal investigator was in charge of the work with the PIONIER instrument. “Infrared interferometry is becoming routinely used to uncover the tiniest details of astronomical objects. Combining this technique with advanced mathematics finally allows us to turn the results of these observations into images.”

Irregularities

- Some findings immediately stand out from the images. “You can see that some spots are brighter or less bright, like in the images above: this hints at processes that can lead to planet formation. For example: there could be instabilities in the disk that can lead to vortices where the disk accumulates grains of space dust that can grow and evolve into a planet.”

- The team will do additional research to identify what might lie behind these irregularities. Kluska will also do new observations to get even more detail and to directly witness planet formation in the regions within the disks that lie close to the star. Additionally, Kluska is heading a team that has started to study 11 disks around other, older types of stars also surrounded by disks of dust, since it is thought these might also sprout planets.

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Figure 11: The protoplanetary disks around the R CrA (left) and HD45677 (right) stars, captured with ESO’s VLT (Very Large Telescope) Interferometer. The orbits are added for reference. The star serves the same purpose, since its light was filtered out to get a more detailed image of the disk (image credit: Jacques Kluska et al.)

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Figure 12: The fifteen images of protoplanetary disks, captured with ESO's Very Large Telescope Interferometer (image credit: KU Leuven, ESO)

• April 16, 2020: Observations made with ESO's Very Large Telescope (VLT) have revealed for the first time that a star orbiting the supermassive black hole at the center of the Milky Way moves just as predicted by Einstein's general theory of relativity. Its orbit is shaped like a rosette and not like an ellipse as predicted by Newton's theory of gravity. This long-sought-after result was made possible by increasingly precise measurements over nearly 30 years, which have enabled scientists to unlock the mysteries of the behemoth lurking at the heart of our galaxy. 21)

- “Einstein’s General Relativity predicts that bound orbits of one object around another are not closed, as in Newtonian Gravity, but precess forwards in the plane of motion. This famous effect — first seen in the orbit of the planet Mercury around the Sun — was the first evidence in favor of General Relativity. One hundred years later we have now detected the same effect in the motion of a star orbiting the compact radio source Sagittarius A* at the center of the Milky Way. This observational breakthrough strengthens the evidence that Sagittarius A* must be a supermassive black hole of 4 million times the mass of the Sun,” says Reinhard Genzel, Director at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany and the architect of the 30-year-long program that led to this result.

- Located 26,000 light-years from the Sun, Sagittarius A* and the dense cluster of stars around it provide a unique laboratory for testing physics in an otherwise unexplored and extreme regime of gravity. One of these stars, S2, sweeps in towards the supermassive black hole to a closest distance less than 20 billion kilometers (one hundred and twenty times the distance between the Sun and Earth), making it one of the closest stars ever found in orbit around the massive giant. At its closest approach to the black hole, S2 is hurtling through space at almost three percent of the speed of light, completing an orbit once every 16 years. “After following the star in its orbit for over two and a half decades, our exquisite measurements robustly detect S2’s Schwarzschild precession in its path around Sagittarius A*,” says Stefan Gillessen of the MPE, who led the analysis of the measurements published today in the journal Astronomy & Astrophysics. 22)

- Most stars and planets have a non-circular orbit and therefore move closer to and further away from the object they are rotating around. S2’s orbit precesses, meaning that the location of its closest point to the supermassive black hole changes with each turn, such that the next orbit is rotated with regard to the previous one, creating a rosette shape. General Relativity provides a precise prediction of how much its orbit changes and the latest measurements from this research exactly match the theory. This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole.

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Figure 13: This artist’s rendition illustrates the Schwarzschild precession of the star’s orbit, with the effect exaggerated for easier visualization (image credit: ESO/L. Calçada)

- The study with ESO’s VLT also helps scientists learn more about the vicinity of the supermassive black hole at the center of our galaxy. “Because the S2 measurements follow General Relativity so well, we can set stringent limits on how much invisible material, such as distributed dark matter or possible smaller black holes, is present around Sagittarius A*. This is of great interest for understanding the formation and evolution of supermassive black holes,” say Guy Perrin and Karine Perraut, the French lead scientists of the project.

- This result is the culmination of 27 years of observations of the S2 star using, for the best part of this time, a fleet of instruments at ESO’s VLT, located in the Atacama Desert in Chile. The number of data points marking the star’s position and velocity attests to the thoroughness and accuracy of the new research: the team made over 330 measurements in total, using the GRAVITY, SINFONI and NACO instruments. Because S2 takes years to orbit the supermassive black hole, it was crucial to follow the star for close to three decades, to unravel the intricacies of its orbital movement.

- The research was conducted by an international team led by Frank Eisenhauer of the MPE with collaborators from France, Portugal, Germany and ESO. The team make up the GRAVITY collaboration, named after the instrument they developed for the VLT Interferometer, which combines the light of all four 8-meter VLT telescopes into a super-telescope (with a resolution equivalent to that of a telescope 130 meters in diameter). The same team reported in 2018 another effect predicted by General Relativity: they saw the light received from S2 being stretched to longer wavelengths as the star passed close to Sagittarius A*. “Our previous result has shown that the light emitted from the star experiences General Relativity. Now we have shown that the star itself senses the effects of General Relativity,” says Paulo Garcia, a researcher at Portugal’s Center for Astrophysics and Gravitation and one of the lead scientists of the GRAVITY project.

- With ESO’s upcoming Extremely Large Telescope, the team believes that they would be able to see much fainter stars orbiting even closer to the supermassive black hole. “If we are lucky, we might capture stars close enough that they actually feel the rotation, the spin, of the black hole,” says Andreas Eckart from Cologne University, another of the lead scientists of the project. This would mean astronomers would be able to measure the two quantities, spin and mass, that characterize Sagittarius A* and define space and time around it. “That would be again a completely different level of testing relativity," says Eckart.

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Figure 14: This simulation shows the orbits of stars very close to the supermassive black hole at the heart of the Milky Way. One of these stars, named S2, orbits every 16 years and is passing very close to the black hole in May 2018. This is a perfect laboratory to test gravitational physics and specifically Einstein's general theory of relativity (image credit: ESO/L. Calçada/spaceengine.org)

• March 11, 2020: Researchers using ESO's Very Large Telescope (VLT) have observed an extreme planet where they suspect it rains iron. The ultra-hot giant exoplanet has a day side where temperatures climb above 2400 degrees Celsius, high enough to vaporise metals. Strong winds carry iron vapor to the cooler night side where it condenses into iron droplets. 23)

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Figure 15: This illustration shows a night-side view of the exoplanet WASP-76b. The ultra-hot giant exoplanet has a day side where temperatures climb above 2400ºC, high enough to vaporise metals. Strong winds carry iron to the cooler night side where it condenses into iron droplets. To the left of the image, we see the evening border of the exoplanet, where it transitions from day to night ( image credit: ESO/M. Kornmesser)

- “One could say that this planet gets rainy in the evening, except it rains iron,” says David Ehrenreich, a professor at the University of Geneva in Switzerland. He led a study, published today in the journal Nature, of this exotic exoplanet. Known as WASP-76b, it is located some 640 light-years away in the constellation of Pisces.

- This strange phenomenon happens because the 'iron rain' planet only ever shows one face, its day side, to its parent star, its cooler night side remaining in perpetual darkness. Like the Moon on its orbit around the Earth, WASP-76b is ‘tidally locked’: it takes as long to rotate around its axis as it does to go around the star.

- On its day side, it receives thousands of times more radiation from its parent star than the Earth does from the Sun. It’s so hot that molecules separate into atoms, and metals like iron evaporate into the atmosphere. The extreme temperature difference between the day and night sides results in vigorous winds that bring the iron vapor from the ultra-hot day side to the cooler night side, where temperatures decrease to around 1500ºC.

- Not only does WASP-76b have different day-night temperatures, it also has distinct day-night chemistry, according to the new study. Using the new ESPRESSO instrument on ESO’s VLT in the Chilean Atacama Desert, the astronomers identified for the first time chemical variations on an ultra-hot gas giant planet. They detected a strong signature of iron vapor at the evening border that separates the planet’s day side from its night side. “Surprisingly, however, we do not see the iron vapor in the morning,” says Ehrenreich. The reason, he says, is that “it is raining iron on the night side of this extreme exoplanet.”

- “The observations show that iron vapor is abundant in the atmosphere of the hot day side of WASP-76b," adds María Rosa Zapatero Osorio, an astrophysicist at the Center for Astrobiology in Madrid, Spain, and the chair of the ESPRESSO science team. "A fraction of this iron is injected into the night side owing to the planet's rotation and atmospheric winds. There, the iron encounters much cooler environments, condenses and rains down."

- This result was obtained from the very first science observations done with ESPRESSO, in September 2018, by the scientific consortium who built the instrument: a team from Portugal, Italy, Switzerland, Spain and ESO.

- ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) was originally designed to hunt for Earth-like planets around Sun-like stars. However, it has proven to be much more versatile. “We soon realized that the remarkable collecting power of the VLT and the extreme stability of ESPRESSO made it a prime machine to study exoplanet atmospheres,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile.

- “What we have now is a whole new way to trace the climate of the most extreme exoplanets,” concludes Ehrenreich. 24) 25)

• February 14, 2020: Betelgeuse has been a beacon in the night sky for stellar observers but it began to dim late last year. At the time of writing Betelgeuse is at about 36% of its normal brightness, a change noticeable even to the naked eye. Astronomy enthusiasts and scientists alike were excitedly hoping to find out more about this unprecedented dimming. 26)

- A team led by Miguel Montargès, an astronomer at KU Leuven (Katholieke Universiteit Leuven — Catholic University of Leuven) in Belgium, has been observing the star with ESO's VLT (Very Large Telescope) since December, aiming to understand why it’s becoming fainter. Among the first observations to come out of their campaign is a stunning new image of Betelgeuse’s surface, taken late last year with the SPHERE instrument.

- The team also happened to observe the star with SPHERE in January 2019, before it began to dim, giving us a before-and-after picture of Betelgeuse. Taken in visible light, the images highlight the changes occurring to the star both in brightness and in apparent shape.

- Many astronomy enthusiasts wondered if Betelgeuse’s dimming meant it was about to explode. Like all red supergiants, Betelgeuse will one day go supernova, but astronomers don’t think this is happening now. They have other hypotheses to explain what exactly is causing the shift in shape and brightness seen in the SPHERE images. “The two scenarios we are working on are a cooling of the surface due to exceptional stellar activity or dust ejection towards us,” says Montargès. “Of course, our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen.”
Note: Betelgeuse's irregular surface is made up of giant convective cells that move, shrink and swell. The star also pulsates, like a beating heart, periodically changing in brightness. These convection and pulsation changes in Betelgeuse are referred to as stellar activity.

- Montargès and his team needed the VLT at Cerro Paranal in Chile to study the star, which is over 700 light-years away, and gather clues on its dimming. “ESO's Paranal Observatory is one of few facilities capable of imaging the surface of Betelgeuse,” he says. Instruments on ESO’s VLT allow observations from the visible to the mid-infrared, meaning astronomers can see both the surface of Betelgeuse and the material around it. “This is the only way we can understand what is happening to the star.”

- Another new image, obtained with the VISIR instrument on the VLT, shows the infrared light being emitted by the dust surrounding Betelgeuse in December 2019. These observations were made by a team led by Pierre Kervella from the Observatory of Paris in France who explained that the wavelength of the image is similar to that detected by heat cameras. The clouds of dust, which resemble flames in the VISIR image, are formed when the star sheds its material back into space.

- “The phrase ‘we are all made of stardust’ is one we hear a lot in popular astronomy, but where exactly does this dust come from?” says Emily Cannon, a PhD student at KU Leuven working with SPHERE images of red supergiants. “Over their lifetimes, red supergiants like Betelgeuse create and eject vast amounts of material even before they explode as supernovae. Modern technology has enabled us to study these objects, hundreds of light-years away, in unprecedented detail giving us the opportunity to unravel the mystery of what triggers their mass loss.”

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Figure 16: The red supergiant star Betelgeuse, in the constellation of Orion, has been undergoing unprecedented dimming. This stunning image of the star’s surface, taken with the SPHERE instrument on ESO’s Very Large Telescope late last year, is among the first observations to come out of an observing campaign aimed at understanding why the star is becoming fainter. When compared with the image taken in January 2019, it shows how much the star has faded and how its apparent shape has changed ( image credit: ESO/M. Montargès et al.)

• December 16, 2019: New observations of the center of our home galaxy have allowed astronomers to reconstruct, for the first time, the history of star formation in the center of the Milky Way. Previously, it had been assumed that stars in the so-called nuclear stellar disk had formed continuously over the past billions of years. Instead, the new results imply a burst of star formation activity more than 8 billion years followed by a quiet period, and then another burst of activity about one billion years ago. The re-written evolutionary history has consequences for the formation of the bar-shaped feature of our galaxy’s disk. The results have been published in the journal Nature Astronomy. 27) 28) 29)

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Figure 17: Taken with the HAWK-I instrument on ESO’s VLT (Very Large Telescope) in the Chilean Atacama Desert, this stunning image shows the Milky Way’s central region with an angular resolution of 0.2 arcseconds. This means the level of detail picked up by HAWK-I is roughly equivalent to seeing a football (soccer ball) in Zurich from Munich, where ESO’s headquarters are located. - The image combines observations in three different wavelength bands. The team used the broadband filters J (centered at 1250 nm, in blue), H (centered at 1635 nm, in green), and Ks (centered at 2150 nm, in red), to cover the near infrared region of the electromagnetic spectrum. By observing in this range of wavelengths, HAWK-I can peer through the dust, allowing it to see certain stars in the central region of our galaxy that would otherwise be hidden (image credit: ESO/Nogueras-Lara et al.)

ESO’s Very Large Telescope (VLT) has observed the central part of the Milky Way with spectacular resolution and uncovered new details about the history of star birth in our galaxy. Thanks to the new observations, astronomers have found evidence for a dramatic event in the life of the Milky Way: a burst of star formation so intense that it resulted in over a hundred thousand supernova explosions.

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Figure 18: This beautiful image of the Milky Way’s central region, taken with the HAWK-I instrument on ESO’s Very Large Telescope, shows interesting features of this part of our galaxy. This image highlights the Nuclear Star Cluster (NSC) right in the center and the Arches Cluster, the densest cluster of stars in the Milky Way. Other features include the Quintuplet cluster, which contains five prominent stars, and a region of ionized hydrogen gas (HII), image credit: ESO/Nogueras-Lara et al.

- "Our unprecedented survey of a large part of the Galactic center has given us detailed insights into the formation process of stars in this region of the Milky Way," says Rainer Schödel from the Institute of Astrophysics of Andalusia in Granada, Spain, who led the observations. "Contrary to what had been accepted up to now, we found that the formation of stars has not been continuous,” adds Francisco Nogueras-Lara, who led two new studies of the Milky Way central region while at the same institute in Granada.

- In the study, published today in Nature Astronomy, the team found that about 80% of the stars in the Milky Way central region formed in the earliest years of our galaxy, between eight and 13.5 billion years ago. This initial period of star formation was followed by about six billion years during which very few stars were born. This was brought to an end by an intense burst of star formation around one billion years ago when, over a period of less than 100 million years, stars with a combined mass possibly as high as a few tens of million Suns formed in this central region.

- “The conditions in the studied region during this burst of activity must have resembled those in ‘starburst’ galaxies, which form stars at rates of more than 100 solar masses per year,” says Nogueras-Lara, who is now based at the Max Planck Institute for Astronomy in Heidelberg, Germany. At present, the whole Milky Way is forming stars at a rate of about one or two solar masses per year.

- “This burst of activity, which must have resulted in the explosion of more than a hundred thousand supernovae, was probably one of the most energetic events in the whole history of the Milky Way,” he adds. During a starburst, many massive stars are created; since they have shorter lifespans than lower-mass stars, they reach the end of their lives much faster, dying in violent supernova explosions.

- This research was possible thanks to observations of the Galactic central region done with ESO’s HAWK-I instrument on the VLT in the Chilean Atacama Desert. This infrared-sensitive camera peered through the dust to give us a remarkably detailed image of the Milky Way’s central region, published in October in Astronomy & Astrophysics by Nogueras-Lara and a team of astronomers from Spain, the US, Japan and Germany. The stunning image shows the galaxy’s densest region of stars, gas and dust, which also hosts a supermassive black hole, with an angular resolution of 0.2 arcseconds. This means the level of detail picked up by HAWK-I is roughly equivalent to seeing a football (soccer ball) in Zurich from Munich, where ESO’s headquarters are located.

- This image is the first release of the GALACTICNUCLEUS survey. This program relied on the large field of view and high angular resolution of HAWK-I on ESO’s VLT to produce a beautifully sharp image of the central region of our galaxy. The survey studied over three million stars, covering an area corresponding to more than 60,000 square light-years at the distance of the Galactic center (one light-year is about 9.5 trillion kilometers).

Bursts of star formation activity (Ref. 27)

- With their result of two intense episodes of star formation, the researchers have rewritten part of our home galaxy’s history: Previously, it had been assumed that the stars in the central region of the Milky Way had formed gradually over the past billions of years. The new timeline has consequences for a number of other astronomical phenomena.

- Notably, it constrains the growth history of our galaxy’s central black hole. Gas flowing into the central regions of our galaxy drive both star formation and the increase in central black hole mass. The newly reconstructed star formation history indicates that our central black hole is likely to have reached most of its present mass earlier than eight billion years ago.

- The brief, but intense burst of star formation activity one billion years ago is likely to be one of the most energetic events in the history of our galaxy. Hundreds of thousands of newly formed massive stars would have exploded as supernovae within millions of years.

- The results also force astronomers to rethink another fundamental feature of our galaxy. The Milky Way is a barred spiral galaxy, with an elongated region estimated between 3,000 and 15,000 light-years long linking the inner ends of its two major spiral arms. Such bar structures are thought to be very efficient at funneling gas into a galaxy’s central region, which would lead to the formation of new stars.

- The billions of years without star formation in the nuclear galactic disk forces astronomers to rethink this scenario. During those quiet years, gas was evidently not funneled into the Galactic center in sufficient amounts. Francisco Nogueras Lara (then Instituto de Astrofísica de Andalucía, now a post-doctoral researcher at MPIA), lead author of the article, says: “Either the galactic bar has come into existence only recently, or such bars are not as efficient in funneling gas as is commonly assumed. In the latter case, some event – like a close encounter with a dwarf galaxy – must have triggered the gas flow towards the Galactic center about one billion years ago.”

Reconstructing the formation history of the Galactic center

- The reconstruction of the history of the nuclear Galactic disk makes use of some of the fundamental insights of astronomers into star formation. Stars only live for a certain span of time, which depends on their mass and chemical composition.

- Whenever many stars have been born at the same time, which is a common occurrence, astronomers can look at the ensemble, plot the star’s brightness against the reddishness of their color (“color-magnitude diagram”) and deduce how long ago the ensemble was formed. One among several age indicators is the “red clump” of stars that have already begun to fuse helium in their core regions. From the average brightness of stars in that clump, one can deduce the age of that group of stars.

Challenges of observing the Galactic center

- But there is a catch: All those techniques require astronomers to study separate stars. For the Milky Way’s central regions, that is a highly challenging task. As seen from Earth, the Galactic center is hidden behind gigantic clouds of dust, requiring infrared observations to “look through” the clouds.

- But then, such observations are bound to see too many stars in the Milky Way’s center! The Galactic center is very dense, with between a thousand and a hundred thousand stars in a cube with a side-length of one light-year. When astronomers observe very dense star fields of this kind, those stellar disks will overlap in the telescope image. Separating such fields into separate stars is difficult – but necessary if you want to reconstruct the formation history of the Galactic center.

The right instrument for the job

- Given those challenges, when Rainer Schödel (Instituto de Astrofísica de Andalucía, PI of the GALACTICNUCLEUS survey), MPIA’s Nadine Neumayer and their colleagues began planning to tackle the history of our Milky Way’s central region in late 2014, they knew they would have to find the right instrument for the job. As Neumayer explains: “We needed a near-infrared instrument with a large field of view, able to observe the Milky Way’s central region which is in the Southern Sky. ESO’s HAWK-I instrument was ideal for our survey.” HAWK-I is an infrared camera at the 8 meter Very Large Telescope at the Paranal Observatory of the European Southern Observatory (ESO) in Chile.

- For their GALACTICNUCLEUS survey, the astronomers observed the Galactic center region with HAWK-I for 16 nights managing to obtain accurate photometry of more than three million stars. Using a special technique known as holographic imaging, the astronomers were able to distinguish between stars as little as 0.2 arc seconds apart. With this accuracy, you could distinguish two one-cent coins viewed from a distance of more than 8 kilometers. Two clearly visible “red clumps” in the resulting color-magnitude diagram allowed for the reconstruction of the formation history of the Galactic nuclear disk.

- As a next step, the astronomers are now studying the influence of dust on their observations (extinction and reddening). Taking into accounts the effect of dust should allow for even more precise reconstructions of the history of our galaxy’s central regions in the future.

• November 21, 2019: An international research team led by scientists from Göttingen and Potsdam proved for the first time that the galaxy NGC 6240 contains three supermassive black holes. The unique observations, published in the journal Astronomy & Astrophysics, show the black holes close to each other in the core of the galaxy. The study points to simultaneous merging processes during the formation of the largest galaxies in the universe. 30)

- Massive Galaxies like the Milky Way typically consist of hundreds of billions of stars and host a black hole with a mass of several million up to several 100 million solar masses at their centers. The galaxy known as NGC 6240 is known as an irregular galaxy due to its particular shape. Until now, astronomers have assumed that it was formed by the collision of two smaller galaxies and therefore contains two black holes in its core. These galactic ancestors moved towards each other at velocities of several 100 km/s and are still in the process of merging. The galaxy system which is around 300 million light years away from us – close by cosmic standards – has been studied in detail at all wavelengths, and has so far been regarded as a prototype for the interaction of galaxies.

- "Through our observations with extremely high spatial resolution we were able to show that the interacting galaxy system NGC 6240 hosts not two – as previously assumed – but three supermassive black holes in its center," reports Professor Wolfram Kollatschny from the University of Göttingen, the lead author of the study. Each of the three heavyweights has a mass of more than 90 million Suns. They are located in a region of space less than 3000 light-years across, i.e. in less than one hundredth of the total size of the galaxy. "Up until now, such a concentration of three supermassive black holes had never been discovered in the universe," adds Dr Peter Weilbacher of the Leibniz Institute for Astrophysics Potsdam (AIP). "The present case provides evidence of a simultaneous merging process of three galaxies along with their central black holes.”

- The discovery of this triple system is of fundamental importance for understanding the evolution of galaxies over time. Until now it has not been possible to explain how the largest and most massive galaxies, which we know from our cosmic environment in the "present time", were formed just by normal galaxy interaction and merging processes over the course of the previous 14 billion years approximately, ie the age of our universe. "If, however, simultaneous merging processes of several galaxies took place, then the largest galaxies with their central supermassive black holes were able to evolve much faster,” Peter Weilbacher summarizes. "Our observations provide the first indication of this scenario.”

- For the unique high-precision observations of the galaxy NGC 6240 using the 8 meter VLT, a telescope operated by ESO (European Southern Observatory)in Chile, the 3D MUSE ((Multi Unit Spectroscopic Explorer) instrument was used in spatial high-resolution mode together with four artificially generated laser stars and an adaptive optics system. Thanks to the sophisticated technology, images are obtained with a sharpness similar to that of the Hubble Space Telescope but additionally contain a spectrum for each image pixel. These spectra were decisive in determining the motion and masses of the supermassive black holes in NGC 6240.

- The scientists assume that the observed, imminent merging of the supermassive black holes in a few million years will also generate very strong gravitational waves. In the foreseeable future, signals of similar objects can be measured with the planned satellite-based gravitational wave detector LISA and further merging systems can be discovered. 31)

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Figure 19: The irregular galaxy NGC 6240. New observations show that it harbors not two but three supermassive black holes at its core. The northern black hole (N) is active and was known before. The zoomed-in new high-spatial resolution image shows that the southern component consists of two supermassive black holes (S1 and S2). The green color indicates the distribution of gas ionized by radiation surrounding the black holes. The red lines show the contours of the starlight from the galaxy and the length of the white bar corresponds to 1000 light years [image credit: P Weilbacher (AIP), NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)]

• October 28, 2019: Astronomers using ESO’s SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument at the VLT (Very Large Telescope) have revealed that the asteroid Hygiea could be classified as a dwarf planet. The object is the fourth largest in the asteroid belt after Ceres, Vesta and Pallas. For the first time, astronomers have observed Hygiea in sufficiently high resolution to study its surface and determine its shape and size. They found that Hygiea is spherical, potentially taking the crown from Ceres as the smallest dwarf planet in the Solar System. 32) 33)

- As an object in the main asteroid belt of our solar system, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neighborhood around its orbit. The final requirement is that it has enough mass for its own gravity to pull it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea.

- “Thanks to the unique capability of the SPHERE instrument on the VLT, which is one of the most powerful imaging systems in the world, we could resolve Hygiea’s shape, which turns out to be nearly spherical,” says lead researcher Pierre Vernazza from the Laboratoire d'Astrophysique de Marseille in France. “Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the Solar System.”

- The team also used the SPHERE observations to constrain Hygiea’s size, putting its diameter at just over 430 km. Pluto, the most famous of dwarf planets, has a diameter close to 2400 km, while Ceres is close to 950 km in size.

- Surprisingly, the observations also revealed that Hygiea lacks the very large impact crater that scientists expected to see on its surface, the team report in the study published today in Nature Astronomy. Hygiea is the main member of one of the largest asteroid families, with close to 7000 members that all originated from the same parent body. Astronomers expected the event that led to the formation of this numerous family to have left a large, deep mark on Hygiea.

- “This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta,” says Vernazza. Although the astronomers observed Hygiea’s surface with a 95% coverage, they could only identify two unambiguous craters. “Neither of these two craters could have been caused by the impact that originated the Hygiea family of asteroids whose volume is comparable to that of a 100 km-sized object. They are too small,” explains study co-author Miroslav Brož of the Astronomical Institute of Charles University in Prague, Czech Republic.

- The team decided to investigate further. Using numerical simulations, they deduced that Hygiea’s spherical shape and large family of asteroids are likely the result of a major head-on collision with a large projectile of diameter between 75 and 150 km. Their simulations show this violent impact, thought to have occurred about 2 billion years ago, completely shattered the parent body. Once the left-over pieces reassembled, they gave Hygiea its round shape and thousands of companion asteroids. “Such a collision between two large bodies in the asteroid belt is unique in the last 3–4 billion years,” says Pavel Ševeček, a PhD student at the Astronomical Institute of Charles University who also participated in the study.

- Studying asteroids in detail has been possible thanks not only to advances in numerical computation, but also to more powerful telescopes. “Thanks to the VLT and the new generation adaptive-optics instrument SPHERE, we are now imaging main belt asteroids with unprecedented resolution, closing the gap between Earth-based and interplanetary mission observations,” Vernazza concludes.

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Figure 20: A new SPHERE/VLT image of Hygiea, which could be the Solar System’s smallest dwarf planet yet. As an object in the main asteroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neighborhood around its orbit. The final requirement is that it have enough mass that its own gravity pulls it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea [image credit: ESO/P. Vernazza et al./MISTRAL algorithm (ONERA/CNRS)]

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Figure 21: New observations with ESO’s SPHERE instrument on the Very Large Telescope have revealed that the surface of Hygiea lacks the very large impact crater that scientists expected to see on its surface. Since it was formed from one of the largest impacts in the history of the asteroid belt, they were expecting to find at least one large, deep impact basin, similar to the one on Vesta (bottom right in the central panel). The new study also found that Hygiea is spherical, potentially taking the crown from Ceres as the smallest dwarf planet in the Solar System. The team used the SPHERE observations to constrain Hygiea’s size, putting its diameter at just over 430 km, while Ceres is close to 950 km in size (image credit: ESO/P. Vernazza et al., L. Jorda et al./MISTRAL algorithm (ONERA/CNRS)

• August 7, 2019: Colorful and wispy, this intriguing collection of objects is known as the Seagull Nebula, named for its resemblance to a gull in flight. Made up of dust, hydrogen, helium and traces of heavier elements, this region is the hot and energetic birthplace of new stars. The remarkable detail captured here by ESO’s VLT Survey Telescope (VST) reveals the individual astronomical objects that make up the celestial bird, as well as the finer features within them. The VST is one of the largest survey telescopes in the world observing the sky in visible light. 34)

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Figure 22: The Rosy Glow of a Cosmic Seagull (image credit: ESO/VPHAS+ team/N.J. Wright (Keele University)

- The main components of the Seagull are three large clouds of gas, the most distinctive being Sharpless 2-296, which forms the “wings”. Spanning about 100 light-years from one wingtip to the other, Sh2-296 displays glowing material and dark dust lanes weaving amid bright stars. It is a beautiful example of an emission nebula, in this case an HII region, indicating active formation of new stars, which can be seen peppering this image.

- It is the radiation emanating from these young stars that gives the clouds their fantastical colors and makes them so eye-catching, by ionizing the surrounding gas and causing it to glow. This radiation is also the main factor that determines the clouds’ shapes, by exerting pressure on the surrounding material and sculpting it into the whimsical morphologies we see. Since each nebula has a unique distribution of stars and may, like this one, be a composite of multiple clouds, they come in a variety of shapes, firing astronomers’ imaginations and evoking comparisons to animals or familiar objects.

- This diversity of shapes is exemplified by the contrast between Sh2-296 and Sh2-292. The latter, seen here just below the “wings”, is a more compact cloud that forms the seagull’s “head”. Its most prominent feature is a huge, extremely luminous star called HD 53367 that is 20 times more massive than the Sun, and which we see as the seagull’s piercing “eye”. Sh2-292 is both an emission nebula and a reflection nebula; much of its light is emitted by ionized gas surrounding its nascent stars, but a significant amount is also reflected from stars outside it.

- The dark swathes that interrupt the clouds’ homogeneity and give them texture are dust lanes – paths of much denser material that hide some of the luminous gas behind them. Nebulae like this one have densities of a few hundred atoms/cm3, much less than the best artificial vacuums on Earth. Nonetheless, nebulae are still much denser than the gas outside them, which has an average density of about 1 atom/cm3.

- The Seagull lies along the border between the constellations of Canis Major (The Great Dog) and Monoceros (The Unicorn), at a distance of about 3700 light-years in one arm of the Milky Way. Spiral galaxies can contain thousands of these clouds, almost all of which are concentrated along their whirling arms.

- Several smaller clouds are also counted as part of the Seagull Nebula, including Sh2-297, which is a small, knotty addition to the tip of the gull’s upper “wing”, Sh2-292 and Sh2-295. These objects are all included in the Sharpless Catalogue, a list of over 300 clouds of glowing gas compiled by American astronomer Stewart Sharpless.

- This image was taken using the VLT Survey Telescope (VST), one of the largest survey telescopes in the world observing the sky in visible light. The VST is designed to photograph large areas of the sky quickly and deeply.

• June 10, 2019: Breakthrough Watch, the global astronomical program looking for Earth-like planets around nearby stars, and the European Southern Observatory (ESO), Europe’s foremost intergovernmental astronomical organization, today announced “first light” on a newly-built planet-finding instrument at ESO’s VLT (Very Large Telescope) in the Atacama Desert, Chile. 35)

- The instrument, called NEAR (Near Earths in the AlphaCen Region), is designed to hunt for exoplanets in our neighboring star system, Alpha Centauri, within the “habitable zones” of its two Sun-like stars, where water could potentially exist in liquid form. It has been developed over the last three years and was built in collaboration with the University of Uppsala in Sweden, the University of Liège in Belgium, the California Institute of Technology in the US, and Kampf Telescope Optics in Munich, Germany. 36)

- Since 23 May ESO’s astronomers at ESO’s VLT have been conducting a ten-day observing run to establish the presence or absence of one or more planets in the star system. Observations will conclude tomorrow, 11 June. Planets in the system (twice the size of Earth or bigger), would be detectable with the upgraded instrumentation. The near- to thermal-infrared range is significant as it corresponds to the heat emitted by a candidate planet, and so enables astronomers to determine whether the planet’s temperature allows liquid water.

- Alpha Centauri is the closest star system to our Solar System, at 4.37 light-years (about 25 trillion miles) away. It consists of two Sun-like stars, Alpha Centauri A and B, plus the red dwarf star, Proxima Centauri. Current knowledge of Alpha Centauri’s planetary systems is sparse. In 2016, a team using ESO instruments discovered one Earth-like planet orbiting Proxima Centauri. But Alpha Centauri A and B remain unknown quantities; it is not clear how stable such binary star systems are for Earth-like planets, and the most promising way to establish whether they exist around these nearby stars is to attempt to observe them.

- Imaging such planets, however, is a major technical challenge, since the starlight that reflects off them is generally billions of times dimmer than the light coming to us directly from their host stars; resolving a small planet close to its star at a distance of several light-years has been compared to spotting a moth circling a street lamp dozens of miles away. To solve this problem, in 2016 Breakthrough Watch and ESO launched a collaboration to build a special instrument called a thermal infrared coronagraph, designed to block out most of the light coming from the star and optimized to capture the infrared light emitted by the warm surface of an orbiting planet, rather than the small amount of starlight it reflects. Just as objects near to the Sun (normally hidden by its glare) can be seen during a total eclipse, so the coronagraph creates a kind of artificial eclipse of its target star, blocking its light and allowing much dimmer objects in its vicinity to be detected. This marks a significant advance in observational capabilities.

- The coronagraph has been installed on one of the VLT’s four 8-meter-aperture telescopes, upgrading and modifying an existing instrument, called VISIR, to optimize its sensitivity to infrared wavelengths associated with potentially habitable exoplanets. It will therefore be able to search for heat signatures similar to that of the Earth, which absorbs energy from the Sun and emits it in the thermal infrared wavelength range. NEAR modifies the existing VISIR instrument in three ways, combining several cutting-edge astronomical engineering achievements. First, it adapts the instrument for coronagraphy, enabling it to drastically reduce the light of the target star and thereby reveal the signatures of potential terrestrial planets. Second, it uses a technique called adaptive optics to strategically deform the telescope’s secondary mirror, compensating for the blur produced by the Earth’s atmosphere. Third, it employs novel chopping strategies that also reduce noise, as well as potentially allowing the instrument to switch rapidly between target stars — as fast as every 100 milliseconds — maximizing the available telescope time.

- Pete Worden, Executive Director of the Breakthrough Initiatives, said: “We’re delighted to collaborate with the ESO in designing, building, installing and now using this innovative new instrument. If there are Earth-like planets around Alpha Centauri A and B, that’s huge news for everyone on our planet.”

- “ESO is glad to bring its expertise, existing infrastructure, and observing time on the Very Large Telescope to the NEAR project,” commented ESO project manager Robin Arsenault.

- “This is a valuable opportunity, as — in addition to its own science goals — the NEAR experiment is also a pathfinder for future planet-hunting instruments for the upcoming Extremely Large Telescope,” says Markus Kasper, ESO’s lead scientist for NEAR.

- “NEAR is the first and (currently) only project that could directly image a habitable exoplanet. It marks an important milestone. Fingers crossed — we are hoping a large habitable planet is orbiting Alpha Cen A or B” commented Olivier Guyon, lead scientist for Breakthrough Watch.

- “Human beings are natural explorers,” said Yuri Milner, founder of the Breakthrough Initiatives, “It is time we found out what lies beyond the next valley. This telescope will let us gaze across.”

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Figure 23: NEAR experiment sees first light. Newly-built planet-finding instrument installed on Very Large Telescope, Chile, begins 100-hour observation of nearby stars Alpha Centauri A and B, aiming to be first to directly image a habitable exoplanet (image credit: ESO)

Notes

The data from the NEAR experiment are publicly available from the ESO archive under program ID 2102.C-5011. A pre-processed and condensed package of all the data will be made available shortly after the campaign concludes. In addition, the Python-based high-contrast imaging data reduction tool PynPoint has been adapted to process NEAR data, and will be provided to members of the astronomical community who would like to use the data but do not have their own data reduction tools. https://pynpoint.readthedocs.io/en/latest/near.html

Breakthrough Watch is a global astronomical program aiming to identify and characterize planets around nearby stars. The program is run by an international team of experts in exoplanet detection and imaging. https://breakthroughinitiatives.org/initiative/4

The Breakthrough Initiatives are a suite of scientific and technological programs, founded by Yuri Milner, investigating life in the Universe. Along with Breakthrough Watch, they include Breakthrough Listen, the largest ever astronomical search for signs of intelligent life beyond Earth, and Breakthrough Starshot, the first significant attempt to design and develop a space probe capable of reaching another star. https://breakthroughinitiatives.org/

• June 3, 2019: The unique capabilities of the SPHERE instrument on ESO’s Very Large Telescope have enabled it to obtain the sharpest images of a double asteroid as it flew by Earth on 25 May. While this double asteroid was not itself a threatening object, scientists used the opportunity to rehearse the response to a hazardous Near-Earth Object (NEO), proving that ESO’s front-line technology could be critical in planetary defence. 37)

- The International Asteroid Warning Network (IAWN) coordinated a cross-organizational observing campaign of the asteroid 1999 KW4 as it flew by Earth, reaching a minimum distance of 5.2 million km on 25 May 2019. 1999 KW4 is about 1.3 km wide, and does not pose any risk to Earth. Since its orbit is well known, scientists were able to predict this fly-by and prepare the observing campaign.

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Figure 24: Side by side observation and artist's impression of Asteroid 1999 KW4

- ESO joined the campaign with its flagship facility, the Very Large Telescope (VLT). The VLT is equipped with SPHERE — one of the very few instruments in the world capable of obtaining images sharp enough to distinguish the two components of the asteroid, which are separated by around 2.6 km.

- SPHERE was designed to observe exoplanets; its state-of-the-art adaptive optics (AO) system corrects for the turbulence of the atmosphere, delivering images as sharp as if the telescope were in space. It is also equipped with coronagraphs to dim the glare of bright stars, exposing faint orbiting exoplanets.

- Taking a break from its usual night job hunting exoplanets, SPHERE data helped astronomers characterize the double asteroid. In particular, it is now possible to measure whether the smaller satellite has the same composition as the larger object.

- “These data, combined with all those that are obtained on other telescopes through the IAWN campaign, will be essential for evaluating effective deflection strategies in the event that an asteroid was found to be on a collision course with Earth,” explained ESO astronomer Olivier Hainaut. “In the worst possible case, this knowledge is also essential to predict how an asteroid could interact with the atmosphere and Earth’s surface, allowing us to mitigate damage in the event of a collision.”

- “The double asteroid was hurtling by the Earth at more than 70,000 km/h, making observing it with the VLT challenging,” said Diego Parraguez, who was piloting the telescope. He had to use all his expertise to lock on to the fast asteroid and capture it with SPHERE.

- Bin Yang, VLT astronomer, declared “When we saw the satellite in the AO-corrected images, we were extremely thrilled. At that moment, we felt that all the pain, all the efforts were worth it.” Mathias Jones, another VLT astronomer involved in these observations, elaborated on the difficulties. “During the observations the atmospheric conditions were a bit unstable. In addition, the asteroid was relatively faint and moving very fast in the sky, making these observations particularly challenging, and causing the AO system to crash several times. It was great to see our hard work pay off despite the difficulties!”

- While 1999 KW4 is not an impact threat, it bears a striking resemblance to another binary asteroid system called Didymos which could pose a threat to Earth sometime in the distant future.

- Didymos and its companion called “Didymoon” are the target of a future pioneering planetary defence experiment. NASA’s DART spacecraft will impact Didymoon in an attempt to change its orbit around its larger twin, in a test of the feasibility of deflecting asteroids. After the impact, ESA’s Hera mission will survey the Didymos asteroids in 2026 to gather key information, including Didymoon’s mass, its surface properties and the shape of the DART crater.

- The success of such missions depends on collaborations between organizations, and tracking Near-Earth Objects is a major focus for the collaboration between ESO and ESA. This cooperative effort has been ongoing since their first successful tracking of a potentially hazardous NEO in early 2014.

- “We are delighted to be playing a role in keeping Earth safe from asteroids,” said Xavier Barcons, ESO’s Director General. “As well as employing the sophisticated capabilities of the VLT, we are working with ESA to create prototypes for a large network to take asteroid detection, tracking and characterization to the next level.”

- “We are delighted to be playing a role in keeping Earth safe from asteroids,” said Xavier Barcons, ESO’s Director General. “As well as employing the sophisticated capabilities of the VLT, we are working with ESA to create prototypes for a large network to take asteroid detection, tracking and characterization to the next level.”

- This recent close encounter with 1999 KW4 comes just a month before Asteroid Day, an official United Nations day of education and awareness about asteroids, to be celebrated on 30 June. Events will be held on five continents, and ESO will be among the major astronomical organizations taking part. The ESO Supernova Planetarium & Visitor Centre will host a range of activities on the theme of asteroids on the day, and members of the public are invited to join in the celebrations.

• May 2, 2019: Gaia, operated by the European Space Agency (ESA), surveys the sky from orbit to create the largest, most precise, three-dimensional map of our Galaxy. One year ago, the Gaia mission produced its much-awaited second data release, which included high-precision measurements — positions, distance and proper motions — of more than one billion stars in our Milky Way galaxy. This catalog has enabled transformational studies in many fields of astronomy, addressing the structure, origin and evolution the Milky Way and generating more than 1700 scientific publications since its launch in 2013. 38)

- In order to reach the accuracy necessary for Gaia’s sky maps, it is crucial to pinpoint the position of the spacecraft from Earth. Therefore, while Gaia scans the sky, gathering data for its stellar census, astronomers regularly monitor its position using a global network of optical telescopes, including the VST at ESO’s Paranal Observatory. The VST is currently the largest survey telescope observing the sky in visible light, and records Gaia’s position in the sky every second night throughout the year.
Note: This collaboration between ESO and ESA is just one of several cooperative projects which have benefitted from the expertise of both organizations in progressing astronomy and astrophysics. On 20 August 2015, the ESA and ESO Directors General signed a cooperation agreement to facilitate synergy through projects such as these.

- “Gaia observations require a special observing procedure,” explained Monika Petr-Gotzens, who has coordinated the execution of ESO’s observations of Gaia since 2013. “The spacecraft is what we call a ‘moving target’, as it is moving quickly relative to background stars — tracking Gaia is quite the challenge!”

- “The VST is the perfect tool for picking out the motion of Gaia,” elaborated Ferdinando Patat, head of the ESO’s Observing Programs Office. “Using one of ESO’s first-rate ground-based facilities to bolster cutting-edge space observations is a fine example of scientific cooperation.”

- “This is an exciting ground-space collaboration, using one of ESO’s world-class telescopes to anchor the trailblazing observations of ESA’s billion star surveyor,” commented Timo Prusti, Gaia project scientist at ESA.

- The VST observations are used by ESA’s flight dynamics experts to track Gaia and refine the knowledge of the spacecraft’s orbit. Painstaking calibration is required to transform the observations, in which Gaia is just a speck of light among the bright stars, into meaningful orbital information. Data from Gaia’s second release was used to identify each of the stars in the field of view, and allowed the position of the spacecraft to be calculated with astonishing precision — up to 20 marcsec (milliarcseconds).

- “This is a challenging process: we are using Gaia’s measurements of the stars to calibrate the position of the Gaia spacecraft and ultimately improve its measurements of the stars,” explains Timo Prusti.

- “After careful and lengthy data processing, we have now achieved the accuracy required for the ground-based observations of Gaia to be implemented as part of the orbit determination,” says Martin Altmann, lead of the Ground Based Optical Tracking (GBOT) campaign at the Center for Astronomy of Heidelberg University, Germany.

- The GBOT information will be used to improve our knowledge of Gaia’s orbit not only in observations to come, but also for all the data that have been gathered from Earth in the previous years, leading to improvements in the data products that will be included in future releases.

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Figure 25: This image, a composite of several observations captured by ESO’s VLT Survey Telescope (VST), shows the ESA spacecraft Gaia as a faint trail of dots across the lower half of the star-filled field of view. These observations were taken as part of an ongoing collaborative effort to measure Gaia’s orbit and improve the accuracy of its unprecedented star map (image credit: ESO)

• March 27, 2019: For the first time, astronomers have succeeded in investigating an exoplanet using optical interferometry. The new method allowed astronomers to measure the position of the exoplanet HR 8799e with unprecedented accuracy. Also, the planet's spectrum was recorded as precisely as never before, paving the way for future searches for life on other planets. The measurements, which were obtained with the participation of astronomers from the Max Planck Institutes for Astronomy and for Extraterrestrial Physics, were performed with the GRAVITY instrument at ESO's Paranal Observatory. 39)

- Investigating exoplanets in detail and without confounding noise is difficult. In general, with increasing distance, it becomes more and more difficult to image fine details of an astronomical object. Furthermore, exoplanets are typically buried in the glare of their much brighter host stars. Now, a group of researchers led by Sylvestre Lacour of the Observatoire de Paris and the Max Planck Institute for Extraterrestrial Physics, also including MPIA researchers, has been able to demonstrate a new method of investigation that mitigates these problems and thereby provides a new perspective on exoplanets.

- Key to the new technique is the GRAVITY instrument, which has been in operation at the European Southern Observatory's Very Large Telescope Interferometer (VLTI) at Paranal Observatory in Chile since 2016. Using a technique known as interferometry, which exploits the wave nature of light, GRAVITY is able to combine the light of several telescopes to form a common image. Combined, the four 8-metre-telescopes of the Very Large Telescope (VLT) can make images so detailed that a single telescope would need to have a mirror diameter of approximately 100 meters to provide the same level of detail.

- The study of the exoplanet HR 8799e that has now been published is the first to demonstrate the potential of interferometric observations for the investigation of exoplanets in practice. The planet is one of only a few (about 120 out of 4000) for which direct images exist; so far, most exoplanets have only been detected indirectly. HR 8977e is part of a young five-body-system, a mere 130 light-years away from us, which consists of the star HR 8799 and four planets (as far as we know, at least). All of the planets are gas giants with between 5 and 10 times the mass of Jupiter.

- This result was announced today in a letter in the journal Astronomy and Astrophysics by the GRAVITY Collaboration, in which they present observations of the exoplanet HR8799e using optical interferometry. The exoplanet was discovered in 2010 orbiting the young main-sequence star HR8799, which lies around 129 light-years from Earth in the constellation of Pegasus. 40) 41)
Note: GRAVITY was developed by a collaboration consisting of the Max Planck Institute for Extraterrestrial Physics (Germany), LESIA of Paris Observatory–PSL / CNRS / Sorbonne Université / Univ. Paris Diderot and IPAG of Université Grenoble Alpes / CNRS (France), the Max Planck Institute for Astronomy (Germany), the University of Cologne (Germany), the CENTRA–Centro de Astrofisica e Gravitação (Portugal) and ESO.

- Today’s result, which reveals new characteristics of HR8799e, required an instrument with very high resolution and sensitivity. GRAVITY can use ESO’s VLT’s four unit telescopes to work together to mimic a single larger telescope using a technique known as interferometry. This creates a super-telescope — the VLTI — that collects and precisely disentangles the light from HR8799e’s atmosphere and the light from its parent star.
Note: Exoplanets can be observed using many different methods. Some are indirect, such as the radial velocity method used by ESO’s exoplanet-hunting HARPS instrument, which measures the pull a planet’s gravity has on its parent star. Direct methods, like the technique pioneered for this result, involve observing the planet itself instead of its effect on its parent star.

- HR8799e is a ‘super-Jupiter’, a world unlike any found in our Solar System, that is both more massive and much younger than any planet orbiting the Sun. At only 30 million years old, this baby exoplanet is young enough to give scientists a window onto the formation of planets and planetary systems. The exoplanet is thoroughly inhospitable — leftover energy from its formation and a powerful greenhouse effect heat HR8799e to a hostile temperature of roughly 1000 °C.

- This is the first time that optical interferometry has been used to reveal details of an exoplanet, and the new technique furnished an exquisitely detailed spectrum of unprecedented quality — ten times more detailed than earlier observations. The team’s measurements were able to reveal the composition of HR8799e’s atmosphere — which contained some surprises.

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Figure 26: This artist’s impression shows the observed exoplanet, which goes by the name HR8799e. The GRAVITY instrument on ESO’s Very Large Telescope Interferometer (VLTI) has made the first direct observation of an exoplanet using optical interferometry. This method revealed a complex exoplanetary atmosphere with clouds of iron and silicates swirling in a planet-wide storm. The technique presents unique possibilities for characterizing many of the exoplanets known today. (image credit: ESO, Luis Calçada)

- “Our analysis showed that HR8799e has an atmosphere containing far more carbon monoxide than methane — something not expected from equilibrium chemistry,” explains team leader Sylvestre Lacour researcher CNRS at the Observatoire de Paris - PSL and the Max Planck Institute for Extraterrestrial Physics. “We can best explain this surprising result with high vertical winds within the atmosphere preventing the carbon monoxide from reacting with hydrogen to form methane.”

- The team found that the atmosphere also contains clouds of iron and silicate dust. When combined with the excess of carbon monoxide, this suggests that HR8799e’s atmosphere is engaged in an enormous and violent storm.

- “Our observations suggest a ball of gas illuminated from the interior, with rays of warm light swirling through stormy patches of dark clouds,” elaborates Lacour. “Convection moves around the clouds of silicate and iron particles, which disaggregate and rain down into the interior. This paints a picture of a dynamic atmosphere of a giant exoplanet at birth, undergoing complex physical and chemical processes.”

- This result builds on GRAVITY’s string of impressive discoveries, which have included breakthroughs such as last year’s observation of gas swirling at 30% of the speed of light just outside the event horizon of the massive Black Hole in the Galactic Centre. It also adds a new way of observing exoplanets to the already extensive arsenal of methods available to ESO’s telescopes and instruments — paving the way to many more impressive discoveries.
Note: Recent exoplanet discoveries made using ESO telescopes include last year’s successful detection of a super-Earth orbiting Barnard’s Star, the closest single star to our Sun, and ALMA’s discovery of young planets orbiting an infant star, which used another novel technique for planet detection.

• March 14, 2019: ESO's Very Large Telescope (VLT) has caught a glimpse of an ethereal nebula hidden away in the darkest corners of the constellation of Orion (The Hunter) — NGC 1788, nicknamed the Cosmic Bat. This bat-shaped reflection nebula doesn’t emit light — instead it is illuminated by a cluster of young stars in its core, only dimly visible through the clouds of dust. Scientific instruments have come a long way since NGC 1788 was first described, and this image taken by the VLT is the most detailed portrait of this nebula ever taken. 42)

- Even though this ghostly nebula in Orion appears to be isolated from other cosmic objects, astronomers believe that it was shaped by powerful stellar winds from the massive stars beyond it. These streams of scorching plasma are thrown from a star’s upper atmosphere at incredible speeds, shaping the clouds secluding the Cosmic Bat’s nascent stars.

- NGC 1788 was first described by the German–British astronomer William Herschel, who included it in a catalogue that later served as the basis for one of the most significant collections of deep-sky objects, the New General Catalogue (NGC). A nice image of this small and dim nebula had already been captured by the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory, but this newly observed scene leaves it in the proverbial dust. Frozen in flight, the minute details of this Cosmic Bat's dusty wings were imaged for the twentieth anniversary of one of ESO's most versatile instruments, the FOcal Reducer and low dispersion Spectrograph 2 (FORS2).
Note 1: In 1864 John Herschel published the General Catalogue of Nebulae and Clusters, which built on extensive catalogues and contained entries for more than five thousand intriguing deep-sky objects. Twenty-four years later, this catalogue was expanded by John Louis Emil Dreyer and published as the New General Catalogue of Nebulae and Clusters of Stars (NGC), a comprehensive collection of stunning deep-sky objects.

- FORS2 is an instrument mounted on Antu, one of the VLT's 8.2-meter Unit Telescopes at the Paranal Observatory, and its ability to image large areas of the sky in exceptional detail has made it a coveted member of ESO's fleet of cutting-edge scientific instruments. Since its first light 20 years ago, FORS2 has become known as “the Swiss army knife of instruments”. This moniker originates from its uniquely broad set of functions [2]. FORS2’s versatility extends beyond purely scientific uses — its ability to capture beautiful high-quality images like this makes it a particularly useful tool for public outreach.
Note 2: In addition to being able to image large areas of the sky with precision, FORS2 can also measure the spectra of multiple objects in the night sky and analyze the polarization of their light. Data from FORS2 are the basis of over 100 scientific studies published every year.

- This image was taken as part of ESO’s Cosmic Gems program, an outreach initiative that uses ESO telescopes to produce images of interesting, intriguing or visually attractive objects for the purposes of education and public outreach. The program makes use of telescope time that cannot be used for science observations, and — with the help of FORS2 — produces breathtaking images of some of the most striking objects in the night sky, such as this intricate reflection nebula. In case the data collected could be useful for future scientific purposes, these observations are saved and made available to astronomers through the ESO Science Archive.

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Figure 27: Hidden in one of the darkest corners of the Orion constellation, this Cosmic Bat is spreading its hazy wings through interstellar space two thousand light-years away. It is illuminated by the young stars nestled in its core — despite being shrouded by opaque clouds of dust, their bright rays still illuminate the nebula. Too dim to be discerned by the naked eye, NGC 1788 reveals its soft colors to ESO's Very Large Telescope in this image — the most detailed to date (image credit: ESO)

Figure 28: Hidden in one of the darkest corners of the Orion constellation, this Cosmic Bat is spreading its hazy wings through interstellar space two thousand light-years away. It is illuminated by the young stars nestled in its core — despite being shrouded by opaque clouds of dust, their bright rays still illuminate the nebula. Too dim to be discerned by the naked eye, NGC 1788 reveals its soft colors to ESO's Very Large Telescope in this image — the most detailed to date (video credit: ESO)

• February 6, 2019: This region of the Large Magellanic Cloud (LMC) glows in striking colors in this image (Figure 29) captured by the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO's Very Large Telescope (VLT). The region, known as LHA 120-N 180B - N180 B for short - is a type of nebula known as an H II region (pronounced "H two"), and is a fertile source of new stars. 43) 44)

- The LMC is a satellite galaxy of the Milky Way, visible mainly from the Southern Hemisphere. At only around 160,000 light-years away from the Earth, it is practically on our doorstep. As well as being close to home, the LMC’s single spiral arm appears nearly face-on, allowing us to inspect regions such as N180 B with ease.

- H II regions are interstellar clouds of ionized hydrogen — the bare nuclei of hydrogen atoms. These regions are stellar nurseries — and the newly formed massive stars are responsible for the ionization of the surrounding gas, which makes for a spectacular sight. N180 B’s distinctive shape is made up of a gargantuan bubble of ionized hydrogen surrounded by four smaller bubbles.

- Deep within this glowing cloud, MUSE has spotted a jet emitted by a fledgling star — a massive young stellar object with a mass 12 times greater than our Sun. The jet — named Herbig–Haro 1177, or HH 1177 for short — is shown in detail in this accompanying image. This is the first time such a jet has been observed in visible light outside the Milky Way, as they are usually obscured by their dusty surroundings. However, the relatively dust-free environment of the LMC allows HH 1177 to be observed at visible wavelengths. At nearly 33 light-years in length, it is one of the longest such jets ever observed.

- HH 1177 tells us about the early lives of stars. The beam is highly collimated; it barely spreads out as it travels. Jets like this are associated with the accretion discs of their star, and can shed light on how fledgling stars gather matter. Astronomers have found that both high- and low-mass stars launch collimated jets like HH 1177 via similar mechanisms — hinting that massive stars can form in the same way as their low-mass counterparts.

- MUSE has recently been vastly improved by the addition of the Adaptive Optics Facility, the Wide Field Mode of which saw first light in 2017. Adaptive optics is the process by which ESO’s telescopes compensate for the blurring effects of the atmosphere — turning twinkling stars into sharp, high-resolution images. Since obtaining these data, the addition of the Narrow Field Mode, has given MUSE vision nearly as sharp as that of the NASA/ESA Hubble Space Telescope — giving it the potential to explore the Universe in greater detail than ever before.

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Figure 29: This dazzling region of newly-forming stars in the Large Magellanic Cloud (LMC) was captured by the MUSE (Multi Unit Spectroscopic Explorer) instrument on ESO’s Very Large Telescope. The relatively small amount of dust in the LMC and MUSE’s acute vision allowed intricate details of the region to be picked out in visible light (image credit: ESO, A McLeod, et al.)

• November 29, 2018: Detailed observations of the quasar 3C 273 with the GRAVITY instrument reveal the structure of rapidly moving gas around the central super-massive black hole, the first time that the so-called “broad line region” could be resolved. The international team of astronomers was thus able to measure the mass of the black hole with unprecedented precision. This measurement confirms the fundamental assumptions of the most commonly used method to measure the mass of central black holes in distant quasars. Studying these black holes and determining their masses is an essential ingredient to understanding galaxy evolution in general. 45)

- An international team of astronomers has now used the GRAVITY instrument to look deep into the heart of the quasar and was able to actually observe the structure of rapidly moving gas around the central black hole. So far, such observations had not been possible due to the small angular size of this inner region, which is about the size of our Solar system but at a distance of some 2.5 billion light years. The GRAVITY instrument combines all four ESO VLT telescopes in a technique called interferometry, which allows a huge gain in angular resolution, equivalent to a telescope with 130 meters in diameter. Thus the astronomers can reveal structures at the level of 10 µas (micro-arcsec), which corresponds to about 0.1 light years at the distance of the quasar (or an object the size of a 1-Euro-coin on the Moon).

- “GRAVITY allowed us to resolve the so-called ‘broad line region’ for the first time ever, and to observe the motion of gas clouds around the central black hole”, explains Eckhard Sturm, lead author from the Max Planck Institute for Extraterrestrial Physics (MPE). “Our observations reveal that the gas clouds do whirl around the central black hole.” 46)

- The broad atomic emission lines are an observational hallmark of quasars, clearly indicating the extra-galactic origin of the source. So far, the size of the broad line region is measured mainly by a method called “reverberation mapping”. Brightness variations of the quasar’s central engine cause a light echo once the radiation hits clouds further out – the larger the size of the system, the later the echo. In the best cases, the motions of the gas can also be identified, often implying a disk in rotation. This result, derived from timing information, can now be confronted with spatially resolved observations with GRAVITY.

- “Our results support the fundamental assumptions of reverberation mapping,” confirms Jason Dexter, co-lead author from MPE. “Information about the motion and size of the region immediately around the black hole are crucial to measure its mass,” he adds. For the first time, the method was now tested experimentally and passed its test with flying colors, confirming previous mass estimates of about 300 million solar masses for the black hole. Thus, GRAVITY provides both a confirmation of the main method used previously to determine black hole masses in quasars and a new and highly accurate, independent method to measure such masses. It thereby promises to provide a benchmark for measuring black hole masses in thousands of other quasars.

- Quasars play a fundamental role in the history of the Universe, as their evolution is intricately tied to galaxy growth. While astronomers assume that basically all large galaxies harbor a massive black hole at their center, so far only the one in our Milky Way has been accessible for detailed studies.

- “This is the first time that we can spatially resolve and study the immediate environs of a massive black hole outside our home galaxy, the Milky Way,” emphasizes Reinhard Genzel, head of the infrared research group at MPE. “Black holes are intriguing objects, allowing us to probe physics under extreme conditions – and with GRAVITY we can now probe them both near and far.”

Figure 30: This animation shows the zoom from an optical image of the quasar to an artistic representation of the surroundings of a supermassive black hole. There is a dusty ring of very hot material collapsing onto the gravity trap and often a jet in which material is ejected at high velocities at the poles. Astronomers have now succeeded in spatially depicting the so-called broad line region, in which gas clouds swirl around the central black hole (video credit: L. Calcada/ESO)

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Figure 31: Powerhouse in space: The quasar 3C273 resides in a giant elliptical galaxy in the constellation of Virgo at a distance of about 2.5 billion light years. It was the first quasar ever to be identified (image credit: ESA/Hubble & NASA)

• November 19, 2018: University of Sydney astronomers, working with international colleagues, have found a star system like none seen before in our galaxy. The scientists believe one of the stars—about 8000 light years from Earth—is the first known candidate in the Milky Way to produce a dangerous gamma-ray burst, among the most energetic events in the universe, when it explodes and dies. 47)

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Figure 32: This is an image of Apep captured at 8 µm in the thermal infrared with the VISIR camera on the European Southern Observatory's VLT telescope, Mt Paranal, Chile. The system can be seen to be a binary, with a much fainter companion to the North of the heart of the system. This companion is not believed to play a role in the sculping of the extended dust plume, about 12 arcseconds across. The origin of this structure comes from the central region, believed itself to contain a binary (the whole thing being a triple star), image credit: Peter Tuthill/University of Sydney/ESO

- The system, comprising a pair of scorchingly luminous stars, was nicknamed Apep by the team after the serpentine Egyptian god of chaos. One star is on the brink of a massive supernova explosion.

- The findings, published today in Nature Astronomy, are controversial as no gamma-ray burst has ever been detected within our own galaxy, the Milky Way. 48)

- Yet in the southern constellation of Norma, nestled just beneath Scorpio's tail, astronomers have discovered this uniquely beautiful star system.

- At its heart, wrapped in an elegantly sculpted plume of dust and gas, lies a powerful binary pair.

- The two hot, luminous stars—known to astronomers as Wolf-Rayets - orbit each other every hundred years or so, according to the research conducted at the Sydney Institute for Astronomy.

- This orbital dance is embossed on a fast wind streaming off the stars. Using spectroscopy, the astronomers have measured the velocity of the stellar winds as fast as 12 million km/hr, about 1 percent the speed of light.

Figure 33: This animated gif is intended to illustrate the geometry of the structure that we have witnessed in the Apep system. From a single image, it is harder to understand the 3-D structure. The central binary (only: not the wider Northern companion in the triple) is illustrated as the blue star at the center. The geometry given is that believed typical for a Wolf-Rayet colliding pinwheel system: that is an optically thin dust plume distributed over the surface of a cone that is dictated by the colliding winds. The whole outflow structure is wrapped into a spiral by the orbital motion of the presumed central binary. Further the dust formation has a specific onset and cessation, which truncate the spiral at the outer and inner limits (for example, giving rise to the notable elliptical hole). Note this is a toy animation to illustrate a fly-around of the structure, and not a model fitted to the data that describes the dust flow process. The looping animation proceeds for about half an orbit (say roughly 60 years) with a pause at about the present epoch. Note that the motion we actually recorded with VISIR in the real data only spans 3 years (image credit: Peter Tuthill/University of Sydney/ESO)

- Dr. Joe Callingham, lead author of the study, said: "We discovered this star as an outlier in a survey with a radio telescope operated by the University of Sydney. We knew immediately we had found something quite exceptional: the luminosity across the spectrum from the radio to the infrared was off the charts." Dr. Callingham is now at the Netherlands Institute for Radio Astronomy. — "When we saw the stunning dust plume coiled around the these incandescent stars, we decided to name it 'Apep' - the monstrous serpent deity and mortal enemy of Sun god Ra from Egyptian mythology."

- That sculpted plume is what makes the system so important, said Professor Peter Tuthill, research group leader at the University of Sydney. "When we saw the spiral dust tail we immediately knew we were dealing with a rare and special kind of nebula called a pinwheel," Professor Tuthill said. "The curved tail is formed by the orbiting binary stars at the center, which inject dust into the expanding wind creating a pattern like a rotating lawn sprinkler. Because the wind expands so much, it inflates the tiny coils of dust revealing the physics of the stars at the heart of the system."

- However, the data on the plume presented a conundrum: the stellar winds were expanding 10 times faster than the dust.

- "It was just astonishing," Professor Tuthill said. "It was like finding a feather caught in a hurricane just drifting along at walking pace."

- Dr. Benjamin Pope, a co-author from New York University, said: "The key to understanding the bizarre behavior of the wind lies in the rotation of the central stars. - What we have found in the Apep system is a supernova precursor that seems to be very rapidly rotating, so fast it might be near break-up."

- Wolf-Rayet stars, like those driving Apep's plume, are known to be very massive stars at the ends of their lives; they could explode as supernovae at any time.

- "The rapid rotation puts Apep into a whole new class. Normal supernovae are already extreme events but adding rotation to the mix can really throw gasoline on the fire."

- The researchers think this might be the recipe for a perfect stellar storm to produce a gamma-ray burst, which are the most extreme events in the Universe after the Big Bang itself. Fortunately, Apep appears not to be aimed at Earth, because a strike by a gamma-ray burst from this proximity could strip ozone from the atmosphere, drastically increasing our exposure to UV light from the Sun.

- "Ultimately, we can't be certain what the future has in store for Apep," Professor Tuthill said. "The system might slow down enough so it explodes as a normal supernova rather than a gamma-ray burst. However, in the meantime, it is providing astronomers a ringside seat into beautiful and dangerous physics that we have not seen before in our galaxy."

• October 31, 2018: ESO’s exquisitely sensitive GRAVITY instrument has added further evidence to the long-standing assumption that a supermassive black hole lurks in the center of the Milky Way. New observations show clumps of gas swirling around at about 30% of the speed of light on a circular orbit just outside its event horizon — the first time material has been observed orbiting close to the point of no return, and the most detailed observations yet of material orbiting this close to a black hole. 49)

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Figure 34: ESO’s GRAVITY instrument on the VLT Interferometer has been used by scientists from a consortium of European institutions, including ESO, to observe flares of infrared radiation coming from the accretion disc around Sagittarius A*, the massive object at the heart of the Milky Way. The observed flares provide long-awaited confirmation that the object in the center of our galaxy is, as has long been assumed, a supermassive black hole. The flares originate from material orbiting very close to the black hole’s event horizon — making these the most detailed observations yet of material orbiting this close to a black hole (image credit: MPE Garching, Observatoire de Paris, Université Grenoble Alpes, CNRS, Max Planck Institute for Astronomy, University of Cologne, Portuguese CENTRA – Centro de Astrofisica e Gravitação and ESO)

- While some matter in the accretion disc — the belt of gas orbiting Sagittarius A* at relativistic speeds — can orbit the black hole safely, anything that gets too close is doomed to be pulled beyond the event horizon. The closest point to a black hole that material can orbit without being irresistibly drawn inwards by the immense mass is known as the innermost stable orbit, and it is from here that the observed flares originate.
Note: Relativistic speeds are those which are so great that the effects of Einstein’s Theory of Relativity become significant. In the case of the accretion disc around Sagittarius A*, the gas is moving at roughly 30% of the speed of light.

- "It’s mind-boggling to actually witness material orbiting a massive black hole at 30% of the speed of light," marvelled Oliver Pfuhl, a scientist at the MPE. "GRAVITY’s tremendous sensitivity has allowed us to observe the accretion processes in realtime in unprecedented detail."

- These measurements were only possible thanks to international collaboration and state-of-the-art instrumentation. The GRAVITY instrument which made this work possible combines the light from four telescopes of ESO’s VLT to create a virtual super-telescope 130 meters in diameter, and has already been used to probe the nature of Sagittarius A*.
Note: GRAVITY was developed by a collaboration consisting of the Max Planck Institute for Extraterrestrial Physics (Germany), LESIA of Paris Observatory–PSL/CNRS/Sorbonne Université/Univ. Paris Diderot and IPAG of Université Grenoble Alpes/CNRS (France), the Max Planck Institute for Astronomy (Germany), the University of Cologne (Germany), the CENTRA–Centro de Astrofísica e Gravitação (Portugal) and ESO.

- Earlier this year, GRAVITY and SINFONI, another instrument on the VLT, allowed the same team to accurately measure the close fly-by of the star S2 as it passed through the extreme gravitational field near Sagittarius A*, and for the first time revealed the effects predicted by Einstein’s general relativity in such an extreme environment. During S2’s close fly-by, strong infrared emission was also observed.

- "We were closely monitoring S2, and of course we always keep an eye on Sagittarius A*," explained Pfuhl. "During our observations, we were lucky enough to notice three bright flares from around the black hole — it was a lucky coincidence!"

- This emission, from highly energetic electrons very close to the black hole, was visible as three prominent bright flares, and exactly matches theoretical predictions for hot spots orbiting close to a black hole of four million solar masses. The flares are thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*.
Note: The solar mass is a unit used in astronomy. It is equal to the mass of our closest star, the Sun, and has a value of 1.989 x 1030 kg. This means that Sgr A* has a mass 1.3 trillion times greater than the Earth.

- Reinhard Genzel, of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, who led the study, explained: "This always was one of our dream projects but we did not dare to hope that it would become possible so soon." Referring to the long-standing assumption that Sagittarius A* is a supermassive black hole, Genzel concluded that "the result is a resounding confirmation of the massive black hole paradigm." 50)

• October 01, 2018: An unexpected abundance of Lyman-alpha emission in the HUDF (Hubble Ultra Deep Field) region was discovered by an international team of astronomers using the MUSE (Multi Unit Spectroscopic Explorer) instrument on ESO’s VLT (Very Large Telescope). The discovered emission covers nearly the entire field of view — leading the team to extrapolate that almost all of the sky is invisibly glowing with Lyman-alpha emission from the early Universe. 51) 52)

- Astronomers have long been accustomed to the sky looking wildly different at different wavelengths, but the extent of the observed Lyman-alpha emission was still surprising. “Realizing that the whole sky glows in optical when observing the Lyman-alpha emission from distant clouds of hydrogen was a literally eye-opening surprise,” explained Kasper Borello Schmidt, a member of the team of astronomers behind this result.

- “This is a great discovery!” added team member Themiya Nanayakkara. “Next time you look at the moonless night sky and see the stars, imagine the unseen glow of hydrogen: the first building block of the universe, illuminating the whole night sky.”

- The HUDF region the team observed is an otherwise unremarkable area in the constellation of Fornax (the Furnace), which was famously mapped by the NASA/ESA Hubble Space Telescope in 2004, when Hubble spent more than 270 hours of precious observing time looking deeper than ever before into this region of space.

- The HUDF observations revealed thousands of galaxies scattered across what appeared to be a dark patch of sky, giving us a humbling view of the scale of the Universe. Now, the outstanding capabilities of MUSE have allowed us to peer even deeper. The detection of Lyman-alpha emission in the HUDF is the first time astronomers have been able to see this faint emission from the gaseous envelopes of the earliest galaxies. This composite image shows the Lyman-alpha radiation in blue superimposed on the iconic HUDF image.

- MUSE, the instrument behind these latest observations, is a state-of-the-art integral field spectrograph installed on Unit Telescope 4 of the VLT at ESO’s Paranal Observatory.
Note: Unit Telescope 4 of the VLT, Yepun, hosts a suite of exceptional scientific instruments and technologically advanced systems, including the Adaptive Optics Facility, which was recently awarded the 2018 Paul F. Forman Team Engineering Excellence Award by the American Optical Society.

When MUSE observes the sky, it sees the distribution of wavelengths in the light striking every pixel in its detector. Looking at the full spectrum of light from astronomical objects provides us with deep insights into the astrophysical processes occurring in the Universe.
Note: The Lyman-alpha radiation that MUSE observed originates from atomic electron transitions in hydrogen atoms which radiate light with a wavelength of around 122 nanometers. As such, this radiation is fully absorbed by the Earth’s atmosphere. Only red-shifted Lyman-alpha emission from extremely distant galaxies has a long enough wavelength to pass through Earth’s atmosphere unimpeded and be detected using ESO’s ground-based telescopes.

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Figure 35: Deep observations made with the MUSE spectrograph on ESO’s VLT have uncovered vast cosmic reservoirs of atomic hydrogen surrounding distant galaxies. The exquisite sensitivity of MUSE allowed for direct observations of dim clouds of hydrogen glowing with Lyman-alpha emission in the early Universe — revealing that almost the whole night sky is invisibly aglow (image credit: eso 1832)

• September 12, 2018: This wonderful image shows the resplendent spiral galaxy NGC 3981 suspended in the inky blackness of space. This galaxy, which lies in the constellation of Crater (the Cup), was imaged in May 2018 using the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument on ESO’s Very Large Telescope (VLT). 53)

- FORS2 is mounted on Unit Telescope 1 (Antu) of the VLT at ESO’s Paranal Observatory in Chile. Amongst the host of cutting-edge instruments mounted on the four Unit Telescopes of the VLT, FORS2 stands apart due to its extreme versatility. This ”Swiss Army knife” of an instrument is able to study a variety of astronomical objects in many different ways — as well as being capable of producing beautiful images like this one.

- The sensitive gaze of FORS2 revealed NGC 3981’s spiral arms, strewn with vast streams of dust and star-forming regions, and a prominent disc of hot young stars. The galaxy is inclined towards Earth, allowing astronomers to peer right into the heart of this galaxy and observe its bright center, a highly energetic region containing a supermassive black hole. Also shown is NGC 3981’s outlying spiral structure, some of which appears to have been stretched outwards from the galaxy, presumably due to the gravitational influence of a past galactic encounter.

- NGC 3981 certainly has many galactic neighbors. Lying approximately 65 million light years from Earth, the galaxy is part of the NGC 4038 group, which also contains the well-known interacting Antennae Galaxies. This group is part of the larger Crater Cloud, which is itself a smaller component of the Virgo Supercluster, the titanic collection of galaxies that hosts our own Milky Way galaxy.

- NGC 3981 is not the only interesting feature captured in this image. As well as several foreground stars from our own galaxy, the Milky Way, FORS2 also captured a rogue asteroid streaking across the sky, visible as the faint line towards the top of the image. This particular asteroid has unwittingly illustrated the process used to create astronomical images, with the three different exposures making up this image displayed in the blue, green and red sections of the asteroid’s path.

- This image was taken as part of ESO’s Cosmic Gems program, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The program makes use of telescope time that cannot be used for science observations. In case the data collected could be useful for future scientific purposes, these observations are saved and made available to astronomers through ESO’s science archive.

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Figure 36: FORS2, an instrument mounted on ESO’s Very Large Telescope, has observed the spiral galaxy NGC 3981 in all its glory. The image was captured as part of the ESO Cosmic Gems Program, which makes use of the rare occasions when observing conditions are not suitable for gathering scientific data. Instead of sitting idle, the ESO Cosmic Gems Program allows ESO’s telescopes to be used to capture visually stunning images of the southern skies (image credit: ESO)

• August 8, 2018: Whereas ESO’s VLT (Very Large Telescope) can observe very faint astronomical objects in great detail, when astronomers want to understand how the huge variety of galaxies come into being they must turn to a different sort of telescope with a much bigger field of view. The VST (VLT Survey Telescope) is such a telescope. It was designed to explore vast swathes of the pristine Chilean night skies, offering astronomers detailed astronomical surveys of the southern hemisphere. 54) 55)

- The powerful surveying properties of the VST led an international team of astronomers to conduct the VST Early-type GAlaxy Survey (VEGAS) [1] to examine a collection of elliptical galaxies in the southern hemisphere [2]. Using the sensitive OmegaCAM detector at the heart of the VST [3], a team led by Marilena Spavone from INAF-Astronomical Observatory of Capodimonte in Naples, Italy, captured images of a wide variety of such galaxies in different environments.
Note 1: VEGAS is a deep multi-band imaging survey of early-type galaxies carried out with the VST (VLT Survey Telescope), led by Enrichetta Iodice from INAF-Astronomical Observatory of Capodimonte in Naples, Italy.
Note 2: Elliptical galaxies are also known as early-type galaxies, not because of their age, but because they were once thought to evolve into the more familiar spiral galaxies, an idea now known to be false. Early-type galaxies are characterized by a smooth ellipsoidal shape and usually a lack of gas and active star formation. The bewildering diversity of shapes and types of galaxy is classified into the Hubble Sequence.
Note 3: OmegaCAM is an exquisitely sensitive detector formed of 32 individual charge coupled devices, and it creates images with 256 million pixels, 16 times greater than the ESA/NASA Hubble Space Telescope’s Advanced Camera for Surveys (ACS). OmegaCAM was designed and built by a consortium including institutes in the Netherlands, Germany and Italy with major contributions from ESO.

- One of these galaxies is NGC 5018, the milky-white galaxy near the center of this image. It lies in the constellation of Virgo (The Virgin) and may at first resemble nothing but a diffuse blob. But, on closer inspection, a tenuous stream of stars and gas — a tidal tail — can be seen stretching outwards from this elliptical galaxy. Delicate galactic features such as tidal tails and stellar streams are hallmarks of galactic interactions, and provide vital clues to the structure and dynamics of galaxies.

- As well as the many elliptical (and a few spiral) galaxies in this remarkable 400-megapixel image, a colorful variety of bright foreground stars in our own Milky Way Galaxy also pepper the image. These stellar interlopers, such as the vividly blue HD 114746 near the center of the image, are not the intended subjects of this astronomical portrait, but happen to lie between the Earth and the distant galaxies under study. Less prominent, but no less fascinating, are the faint tracks left by asteroids in our own Solar System. Just below NGC 5018, the faint streak left by the asteroid 2001 TJ21 (110423) — captured over several successive observations — can be seen stretching across the image. Further to the right, another asteroid — 2000 WU69 (98603) — left its trace in this spectacular image.

- While astronomers set out to investigate the delicate features of distant galaxies millions of light-years from Earth, in the process they also captured images of nearby stars hundreds of light-years away, and even the faint trails of asteroids only light-minutes away in our own Solar System. Even when studying the furthest reaches of the cosmos, the sensitivity of ESO telescopes and dark Chilean skies can offer entrancing observations much closer to home.

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Figure 37: A glittering host of galaxies populate this rich image taken with ESO’s VST (VLT Survey Telescope), a state-of-the-art 2.6-m telescope designed for surveying the sky in visible light. The features of the multitude of galaxies strewn across the image allow astronomers to uncover the most delicate details of galactic structure (image credit: eso1827 — Photo Release)

• July 26, 2018: First Successful Test of Einstein’s General Relativity Near Supermassive Black Hole. Obscured by thick clouds of absorbing dust, the closest supermassive black hole to the Earth lies 26 000 light-years away at the center of the Milky Way. This gravitational monster, which has a mass four million times that of the Sun, is surrounded by a small group of stars orbiting around it at high speed. This extreme environment — the strongest gravitational field in our galaxy — makes it the perfect place to explore gravitational physics, and particularly to test Einstein’s general theory of relativity. 56)

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Figure 38: Artist’s impression of S2 passing supermassive black hole at the center of the Milky Way. Observations made with ESO’s VLT (Very Large Telescope) have for the first time revealed the effects predicted by Einstein’s general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the center of the Milky Way. This long-sought result represents the climax of a 26-year-long observation campaign using ESO’s telescopes in Chile (image credit: ESO, M. Kommesser)

- New infrared observations from the exquisitely sensitive GRAVITY, SINFONI and NACO instruments on ESO’s VLT have now allowed astronomers to follow one of these stars, called S2, as it passed very close to the black hole during May 2018. At the closest point this star was at a distance of less than 20 billion kilometers from the black hole and moving at a speed in excess of 25 million kilometers per hour — almost three percent of the speed of light. 57)
Note 1: GRAVITY was developed in a collaboration by the Max Planck Institute for extraterrestrial Physics, LESIA of Paris Observatory /CNRS/Sorbonne Université/Univ. Paris Diderot and IPAG of Université Grenoble Alpes/CNRS, the Max Planck Institute for Astronomy, the University of Cologne, the CENTRA – Centro de Astrofisica e Gravitação, and ESO (European Southern Observatory).
Note 2: S2 (Source 2 - a star that is located close to the radio source Sagittarius A) orbits the black hole every 16 years in a highly eccentric orbit that brings it within twenty billion kilometers — 120 times the distance from Earth to the Sun, or about four times the distance from the Sun to Neptune — at its closest approach to the black hole. This distance corresponds to about 1500 times the Schwarzschild radius of the black hole itself.

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Figure 39: Orbit diagram of S2 around the supermassive black hole at the center of the Milky Way. It was compiled from observations with ESO telescopes and instruments over a period of more than 25 years. The star takes 16 years to complete one orbit and was very close to the black hole in May 2018 (image credit: ESO/MPE/GRAVITY Collaboration)

- The team compared the position and velocity measurements from GRAVITY and SINFONI respectively, along with previous observations of S2 using other instruments, with the predictions of Newtonian gravity, general relativity and other theories of gravity. The new results are inconsistent with Newtonian predictions and in excellent agreement with the predictions of general relativity.

- These extremely precise measurements were made by an international team led by Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, in conjunction with collaborators around the world, at the Paris Observatory–PSL, the Université Grenoble Alpes, CNRS, the Max Planck Institute for Astronomy, the University of Cologne, the Portuguese CENTRA – Centro de Astrofisica e Gravitação and ESO. The observations are the culmination of a 26-year series of ever-more-precise observations of the center of the Milky Way using ESO instruments.
Note: Observations of the center of the Milky Way must be made at longer wavelengths (in this case infrared) as the clouds of dust between the Earth and the central region strongly absorb visible light.

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Figure 40: Cosmic swarm of bees: This simulation shows the orbits of stars very close to the supermassive black hole at the heart of the Milky Way. One of these stars, named S2, orbits every 16 years and is passing very close to the black hole in May 2018 (image credit: ESO/L. Calçada/spaceengine.org)

- “This is the second time that we have observed the close passage of S2 around the black hole in our galactic center. But this time, because of much improved instrumentation, we were able to observe the star with unprecedented resolution,” explains Genzel. “We have been preparing intensely for this event over several years, as we wanted to make the most of this unique opportunity to observe general relativistic effects.”

- The new measurements clearly reveal an effect called gravitational redshift. Light from the star is stretched to longer wavelengths by the very strong gravitational field of the black hole. And the change in the wavelength of light from S2 agrees precisely with that predicted by Einstein’s theory of general relativity. This is the first time that this deviation from the predictions of the simpler Newtonian theory of gravity has been observed in the motion of a star around a supermassive black hole.

- The team used SINFONI to measure the velocity of S2 towards and away from Earth and the GRAVITY instrument in the VLT Interferometer (VLTI) to make extraordinarily precise measurements of the changing position of S2 in order to define the shape of its orbit. GRAVITY creates such sharp images that it can reveal the motion of the star from night to night as it passes close to the black hole — 26 000 light-years from Earth.

- “Our first observations of S2 with GRAVITY, about two years ago, already showed that we would have the ideal black hole laboratory,” adds Frank Eisenhauer (MPE), Principal Investigator of GRAVITY and the SINFONI spectrograph. “During the close passage, we could even detect the faint glow around the black hole on most of the images, which allowed us to precisely follow the star on its orbit, ultimately leading to the detection of the gravitational redshift in the spectrum of S2.”

- More than one hundred years after he published his paper setting out the equations of general relativity, Einstein has been proved right once more — in a much more extreme laboratory than he could have possibly imagined!

- Françoise Delplancke, head of the System Engineering Department at ESO, explains the significance of the observations: “Here in the Solar System we can only test the laws of physics now and under certain circumstances. So it’s very important in astronomy to also check that those laws are still valid where the gravitational fields are very much stronger.”

- Continuing observations are expected to reveal another relativistic effect very soon — a small rotation of the star’s orbit, known as Schwarzschild precession — as S2 moves away from the black hole.

- Xavier Barcons, ESO’s Director General, concludes: “ESO has worked with Reinhard Genzel and his team and collaborators in the ESO Member States for over a quarter of a century. It was a huge challenge to develop the uniquely powerful instruments needed to make these very delicate measurements and to deploy them at the VLT in Paranal. The discovery announced today is the very exciting result of a remarkable partnership.”

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Figure 41: This diagram shows the motion of the star S2 as it passes close to the supermassive black hole at the center of the Milky Way. It was compiled from observations with the GRAVITY instrument in the VLT interferometer. At this point the star was travelling at nearly 3% of the speed of light and its shift in position can be seen from night to night. The sizes of the star and the black hole are not to scale (image credit: ESO/MPE/GRAVITY Collaboration) 58)

• July 18,2018: ESO's VLT has achieved first light with a new adaptive optics mode called laser tomography — and has captured remarkably sharp test images of the planet Neptune, star clusters and other objects. The pioneering MUSE instrument in Narrow-Field Mode, working with the GALACSI adaptive optics module, can now use this new technique to correct for turbulence at different altitudes in the atmosphere. It is now possible to capture images from the ground at visible wavelengths that are sharper than those from the NASA/ESA Hubble Space Telescope. The combination of exquisite image sharpness and the spectroscopic capabilities of MUSE will enable astronomers to study the properties of astronomical objects in much greater detail than was possible before. 59)

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Figure 42: This image of the planet Neptune was obtained during the testing of the Narrow-Field adaptive optics mode of the MUSE/GALACSI instrument on ESO’s Very Large Telescope. The corrected image is sharper than a comparable image from the NASA/ESA Hubble Space Telescope (image credit: ESO/P. Weilbacher (AIP))

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Figure 43: Neptune from the VLT with and without adaptive optics (image credit: ESO)

- The MUSE (Multi Unit Spectroscopic Explorer) instrument on ESO’s Very Large Telescope (VLT) works with an adaptive optics unit called GALACSI (Ground Atmospheric Layer Adaptive Optics for Spectroscopic Imaging). This makes use of the Laser Guide Star Facility, 4LGSF, a subsystem of the AOF (Adaptive Optics Facility). The AOF provides adaptive optics for instruments on the VLT's Unit Telescope 4 (UT4). MUSE was the first instrument to benefit from this new facility and it now has two adaptive optics modes — the Wide Field Mode and the Narrow Field Mode.
Note: MUSE and GALACSI in Wide-Field Mode already provides a correction over a 1.0 arcmin wide field of view, with pixels 0.2 x 0.2 arcsec in size. This new Narrow-Field Mode from GALACSI covers a much smaller 7.5 arcsec FOV, but with much smaller pixels just 0.025 x 0.025 arcsec to fully exploit the exquisite resolution.

- The MUSE Wide Field Mode coupled to GALACSI in ground-layer mode corrects for the effects of atmospheric turbulence up to 1 km above the telescope over a comparatively wide field of view. But the new Narrow Field Mode using laser tomography corrects for almost all of the atmospheric turbulence above the telescope to create much sharper images, but over a smaller region of the sky.
Note: Atmospheric turbulence varies with altitude; some layers cause more degradation to the light beam from stars than others. The complex adaptive optics technique of Laser Tomography aims to correct mainly the turbulence of these atmospheric layers. A set of pre-defined layers are selected for the MUSE/GALACSI Narrow Field Mode at 0 km (ground layer; always an important contributor), 3, 9 and 14 km altitude. The correction algorithm is then optimized for these layers to enable astronomers to reach an image quality almost as good as with a natural guide star and matching the theoretical limit of the telescope.

- With this new capability, the 8 m UT4 reaches the theoretical limit of image sharpness and is no longer limited by atmospheric blur. This is extremely difficult to attain in the visible and gives images comparable in sharpness to those from the NASA/ESA Hubble Space Telescope. It will enable astronomers to study in unprecedented detail fascinating objects such as supermassive black holes at the centers of distant galaxies, jets from young stars, globular clusters, supernovae, planets and their satellites in the Solar System and much more.

- Adaptive optics is a technique to compensate for the blurring effect of the Earth’s atmosphere, also known as astronomical seeing, which is a big problem faced by all ground-based telescopes. The same turbulence in the atmosphere that causes stars to twinkle to the naked eye results in blurred images of the Universe for large telescopes. Light from stars and galaxies becomes distorted as it passes through our atmosphere, and astronomers must use clever technology to improve image quality artificially.

- To achieve this, four brilliant lasers are fixed to UT4 that project columns of intense orange light 30 cm in diameter into the sky, stimulating sodium atoms high in the atmosphere and creating artificial Laser Guide Stars. Adaptive optics systems use the light from these “stars” to determine the turbulence in the atmosphere and calculate corrections one thousand times per second, commanding the thin, deformable secondary mirror of UT4 to constantly alter its shape, correcting for the distorted light.

- MUSE is not the only instrument to benefit from the Adaptive Optics Facility. Another adaptive optics system, GRAAL (GRound layer Adaptive optics Assisted by Lasers), is already in use with the infrared camera HAWK-I. This will be followed in a few years by the powerful new instrument ERIS (Enhanced Resolution Imager and Spectrograph). Together these major developments in adaptive optics are enhancing the already powerful fleet of ESO telescopes, bringing the Universe into focus.

- This new mode also constitutes a major step forward for the ESO’s Extremely Large Telescope, which will need Laser Tomography to reach its science goals. These results on UT4 with the AOF will help to bring ELT’s engineers and scientists closer to implementing similar adaptive optics technology on the 39 meter giant.

• July 11, 2018: New observations with ESO’s Very Large Telescope show the star cluster RCW 38 in all its glory (Figure 44). This image was taken during testing of the HAWK-I (High Acuity Wide field K-band Imager) camera with the GRAAL [(Ground-layer AOM (Adaptive Optics Module) Assisted by Lasers)] adaptive optics system. It shows RCW 38 and its surrounding clouds of brightly glowing gas in exquisite detail, with dark tendrils of dust threading through the bright core of this young gathering of stars. 60)

- The central area of RCW 38 is visible here as a bright, blue-tinted region, an area inhabited by numerous very young stars and protostars that are still in the process of forming. The intense radiation pouring out from these newly born stars causes the surrounding gas to glow brightly. This is in stark contrast to the streams of cooler cosmic dust winding through the region, which glow gently in dark shades of red and orange. The contrast creates this spectacular scene — a piece of celestial artwork.

- Previous images of this region taken in optical wavelengths are strikingly different — optical images appear emptier of stars due to dust and gas blocking our view of the cluster. Observations in the infrared, however, allow us to peer through the dust that obscures the view in the optical and delve into the heart of this star cluster.

- HAWK-I is installed on Unit Telescope 4 (Yepun) of the VLT, and operates at near-infrared wavelengths. It has many scientific roles, including obtaining images of nearby galaxies or large nebulae as well as individual stars and exoplanets. GRAAL is an adaptive optics module which helps HAWK-I to produce these spectacular images. It makes use of four laser beams projected into the night sky, which act as artificial reference stars, used to correct for the effects of atmospheric turbulence — providing a sharper image.

- This image was captured as part of a series of test observations — a process known as science verification — for HAWK-I and GRAAL. These tests are an integral part of the commissioning of a new instrument on the VLT, and include a set of typical scientific observations that verify and demonstrate the capabilities of the new instrument.

- The Science Verification of HAWK-I with the GRAAL adaptive optics module was presented in an article in ESO’s quarterly journal ”The Messenger” entitled HAWK-I GRAAL Science Verification. 61)

- The Principal Investigator of the observing proposal which led this spectacular image was Koraljka Muzic (CENTRA, University of Lisbon, Portugal). Her collaborators were Joana Ascenso (CENTRA, University of Porto, Portugal), Amelia Bayo (University of Valparaiso, Chile), Arjan Bik (Stockholm University, Sweden), Hervé Bouy (Laboratoire d’astrophysique de Bordeaux, France), Lucas Cieza (University Diego Portales, Chile), Vincent Geers (UKATC, UK), Ray Jayawardhana (York University, Canada), Karla Peña Ramírez (University of Antofagasta, Chile), Rainer Schoedel (Instituto de Astrofísica de Andalucía, Spain), and Aleks Scholz (University of St Andrews, UK).

- The science verification team was composed of Bruno Leibundgut, Pascale Hibon, Harald Kuntschner, Cyrielle Opitom, Jerome Paufique, Monika Petr-Gotzens, Ralf Siebenmorgen, Elena Valenti and Anita Zanella, all from ESO.

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Figure 44: This image shows the star cluster RCW 38, as captured by the HAWK-I infrared imager mounted on ESO’s VLT (Very Large Telescope) in Chile. By gazing into infrared wavelengths, HAWK-I can examine dust-shrouded star clusters like RCW 38, providing an unparalleled view of the stars forming within. This cluster contains hundreds of young, hot, massive stars, and lies some 5500 light-years away in the constellation of Vela (The Sails), image credit: