Minimize Hubble

HST (Hubble Space Telescope) Mission

Sensor Complement   HST Imagery    References 

The HST (Hubble Space Telescope) of NASA is named in honor of the American astronomer Edwin Hubble (1889-1953), Dr. Hubble confirmed an "expanding" universe, which provided the foundation for the big-bang theory. Hubble, the observatory, is the first major optical telescope to be placed in space, the ultimate mountaintop. Above the distortion of the atmosphere, far far above rain clouds and light pollution, Hubble has an unobstructed view of the universe. Scientists have used Hubble to observe the most distant stars and galaxies as well as the planets in our solar system. 1)

The planning for HST started in the early 1970s. The HST was launched into LEO (Low Earth Orbit) on April 24, 1990 on STS-31 (12:33:51 UTC, on Shuttle Discovery). Hubble is operational as of 2019, in its 30th year on orbit, and is one of NASA's Great Observatories. Hubble's launch and deployment in April 1990 marked the most significant advance in astronomy since Galileo's telescope. Thanks to five servicing missions and more than 25 years of operation, our view of the universe and our place within it has never been the same.

Mission:

• Deployment of Hubble: April 25, 1990

• First Image: May 20, 1990: Star cluster NGC 3532

• Servicing Mission 1 (STS-61): December 1993

• Servicing Mission 2 (STS-82): February 1997

• Servicing Mission 3A (STS-103): December 1999

• Servicing Mission 3B (STS-109): February 2002

• Servicing Mission 4 (STS-125): May 2009

Spacecraft: The spacecraft has a length of 13.2 m, a mass at launch of 10,886 kg, post SM (Servicing Mission) 4 of 12,247 kg, and a maximum diameter of 4.2 m.

Orbit: LEO with an altitude of 547 km an inclination of 28.5º, and a period of 95 minutes.

The HST (Hubble Space Telescope) of NASA features a ULE TM(Ultra-Low Expansion) primary mirror of 2.4 m diameter (f/24 Ritchey-Chretien) and a 0.3 m Zerodur secondary mirror. The HST primary mirror was a lightweighted monolithic design (824 kg) by Perkin-Elmer (now Goodrich Inc.), Danbury, CN, using a lightweight, thick egg crate core sandwiched between two plates and fused together.

The HST is the most precisely pointed instrument in spaceborne astronomy. The pointing requirements call for a continuous 24 hour target lock maintenance of 0.007 arcseconds (2 millionth degree).

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Figure 1: IMAX Cargo Bay Camera view of the Hubble Space Telescope at the moment of release, mission STS-31 in April 1990 (image credit: NASA)

Some background:

The telescope's original equipment package included the Wide Field/Planetary Camera (WF/PC), Goddard High Resolution Spectograph (GHRS), Faint Object Camera (FOC), Faint Object Spectograph (FOS), and High Speed Photometer (HSP). 2) 3)

After a few weeks of operation, scientists noticed that images being sent back from Hubble were slightly blurred. While this distortion still allowed scientists to study the cosmos and make significant discoveries, it resulted in less spectacular images, and some of the original mission could not be fulfilled. An investigation finally revealed a spherical aberration in the primary mirror, due to a miscalibrated measuring instrument that caused the edges of the mirror to be ground slightly too flat. Engineers rushed to come up with a fix to the problem in time for Hubble's first scheduled servicing mission in 1993. The system designed to correct the error was designated COSTAR (Corrective Optics Space Telescope Axial Replacement). COSTAR was a set of optics that compensated for the aberration and would allow all of Hubble's instruments to function normally.

In December, 1993, the crew of STS-61 embarked on a service mission to replace a number of Hubble's parts. Following intensive training on the use of new tools never used before in space, two teams of astronauts completed repairs during a record five back-to-back spacewalks. During the EVAs, COSTAR was installed and the Wide Field/Planetary Camera was replaced with the Wide Field/Planetary Camera 2, which was designed to compensate for the mirror problem. The team also performed basic maintenance on the craft, installed new solar arrays, and replaced four of Hubble's gyroscopes.

Shortly after the crew returned to Earth and the Hubble Space Telescope began returning sharp and spectacular images, NASA deemed the servicing mission a success. Astronomers could now take advantage of a fully functional space telescope, and the public was treated to breathtaking photos of stars, galaxies, nebulae, and other deep-space objects. Subsequent servicing missions improved Hubble's capabilities and performed routine repairs.

In February, 1997, the crew of STS-82 installed the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) and the Space Telescope Imaging Spectograph (STIS) to detect infrared light from deep-space objects and take detailed photos of celestial objects. Servicing mission 3A in December, 1999 replaced all six of the telescope's aging gyroscopes, which accurately point the telescope at its target. STS-103 astronauts also replaced one of the telescope's three fine guidance sensors and installed a new computer, all in time to redeploy Hubble into orbit on Christmas Day. The most recent servicing mission to the spacecraft, servicing mission 3B, came aboard STS-109 in March, 2002. Columbia crewmembers installed the new Advanced Camera for Surveys (ACS), which had sharper vision, a wider field of view, and quicker data gathering than the Wide Field/Planetary Camera 2. Astronauts also replaced Hubble's solar panels with a more efficient array and conducted repairs on the NICMOS.

STS109-E-5700 (9 March 2002) — The Hubble Space Telescope, sporting new solar arrays and other important but less visible new hardware, begins its separation from the Space Shuttle Columbia. The STS-109 crew deployed the giant telescope at 4:04 a.m. CST (1004 GMT), March 9, 2002. Afterward, the seven crew members began to focus their attention to the trip home, scheduled for March 12. The STS-109 astronauts conducted five space walks to service and upgrade Hubble. 4)

The power for the NASA/ESA Hubble Space Telescope's scientific discoveries comes from solar cells. Designing and constructing Hubble's first two sets of solar cell arrays, and the accompanying Solar Array Drive Mechanism (SADM) and Solar Array Drive Electronics (SADE), constituted a huge technological achievement for the European Space Agency (ESA) and European industry. After an in-orbit life of more than 10 years, the ESA-built solar arrays were replaced by new, more powerful arrays. However, ESA’s SADM and SADE, which control the telescope’s current solar arrays, are still on board and under ESA purview. They are among the telescope’s oldest subsystems. 5)

In December 2019, the accumulated slew angles of the SADM had reached 1,000,000 degrees of travel. This travel began accumulating on this day 18 years ago, 5 March 2002, when ESA’s solar arrays were replaced during the Space Shuttle Servicing Mission 3B.

“This milestone is a special occasion to recognize that after all of these years of operation, the SADM and SADE are still functioning perfectly without any sign of degradation. It's a fantastic achievement,” said Lothar Gerlach, former ESA project manager for the European hardware onboard the Hubble Space Telescope. “The SADM and SADE have greatly exceeded their design life, and we are very proud they are still a key part of Hubble scientific operations”.

Notes: The Hubble Space Telescope is a project of international co-operation between ESA and NASA. The ESA Hubble Space Telescope solar arrays have been provided to the European Space Agency by Astrium (UK/Germany — formerly British Aerospace, United Kingdom, AEG/Telefunken and Dornier — now Airbus, Germany), and Oerlikon Contraves Space (Switzerland).

Europe & Hubble 6)

ESA’s contribution to the Hubble Project guarantees European scientists access to 15% of Hubble observing time. Hubble time is allocated on scientific merit by an international panel that includes European experts. Over Hubble’s lifetime, European astronomers have, in open competition, been allocated more than the guaranteed 15%, and in some years the proportion has been closer to 25%.

Europe also provided one of the scientific instruments Hubble was launched with, designed Hubble’s solar panels, and has provided astronauts to participate in servicing missions.

Scientists from most ESA Member States have had an opportunity to observe with Hubble. To date, almost 800 observing programs with European principal investigators (lead scientists) have been carried out or are scheduled to be in the next observing round, with many others involved as co-investigators.

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Figure 2: An overview of the fraction of observing time that has been rewarded to ESA proposals. It is measured in two different ways: In number of proposals and in time (here measured in units of Hubble orbits, i.e. 96 minutes). By both metrics, European scientists have won comfortably more than 15% of observing time in the majority of years since launch (image credit: ESA)

The success of a scientific mission can be measured by the number and quality of scientific papers that are published in the specialized press. The number of papers based on Hubble observations published each year has been increasing continuously since the telescope’s launch. There is at least one European author or co-author on about 30% of these papers, indicating the importance of Hubble to European astronomy.

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Figure 3: This photograph of NASA’s Hubble Space Telescope was taken on the fifth servicing mission to the observatory in May 2009 (image credit: NASA)

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Figure 4: Artist's view of the HST in space along with the designation of the key element locations (image credit: NASA)

The Hubble Space Telescope is an international collaboration among NASA and ESA (European Space Agency). NASA has overall responsibility for the Hubble mission and operations. ESA provided the original FOC (Faint Object Camera) and solar panels, and provides science operations support.

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Figure 5: Photo of the Hubble mission operations team at NASA's Goddard Space Flight Center in Greenbelt, Maryland, as of Hubble’s 25th anniversary of flight in April 2015. Since Hubble’s official start in 1977, thousand of people from the United States and Europe have supported the mission through building and testing hardware and software, operating the vehicle, and performing science operations. More than 30 astronauts have flown to Hubble to deploy, upgrade and repair the observatory with the support of a human spaceflight and space shuttle staff. Thousands of astronomers from dozens of countries have used Hubble and analyzed its data to produce more than 15,000 peer reviewed papers to date (image credit: NASA/GSFC, Bill Hrybyk) 7)


Note: At this stage of the mission (2018), no attempt is being made to recover all facets of Hubble regarding the spacecraft, instrumentation and the past history (it would have required a constant accompaniment of the mission with all updates over its lifetime). Instead, some fairly recent images of the mission and the operational status of the mission are presented.

The Hubble Servicing Missions are shortly described in a separate chapter of this file.




HST sensor complement: (ACS, WFC3, STIS, COS, FGS, NICMOS)

The Hubble Space Telescope has three types of instruments that analyze light from the universe: cameras, spectrographs and interferometers. 8)

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Figure 6: Hubble’s scientific instruments analyze different types of light ranging from ultraviolet (UV) to infrared (IR). This graphic shows which wavelengths each instrument studies (image credit: NASA)


Cameras:

Hubble has two primary camera systems to capture images of the cosmos. Called the Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3), these two systems work together to provide superb wide-field imaging over a broad range of wavelengths.

ACS (Advanced Camera for Surveys)

Installed on Hubble in 2002, ACS was designed primarily for wide-field imagery in visible wavelengths, although it can also detect ultraviolet and near-infrared light. ACS has three cameras, called channels, that capture different types of images. An electronics failure in January 2007 rendered the two most-used science channels inoperable. In 2009, astronauts were able to repair one of the channels and restored ACS’s capacity to capture high-resolution, wide-field views.

WFC3 (Wide Field Camera 3)

Installed in 2009, WFC3 provides wide-field imagery in ultraviolet, visible and infrared light. WFC3 was designed to complement ACS and expand the imaging capabilities of Hubble in general. While ACS is primarily used for visible-light imaging, WFC3 probes deeper into infrared and ultraviolet wavelengths, providing a more complete view of the cosmos.

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Figure 7: Astronaut Andrew Feustel prepares to install WFC3 (Wide Field Camera 3) on Hubble during Servicing Mission 4 in 2009 (image credit: NASA)


Spectrographs

Spectrographs practice spectroscopy, the science of breaking light down to its component parts, similar to how a prism splits white light into a rainbow. Any object that absorbs or emits light can be studied with a spectrograph to determine characteristics such as temperature, density, chemical composition and velocity.

Hubble currently utilizes two spectrographs: COS (Cosmic Origins Spectrograph) and the STIS (Space Telescope Imaging Spectrograph). COS and STIS are complementary instruments that provide scientists with detailed spectral data for a variety of celestial objects. While STIS is a versatile, “all purpose” spectrograph that handles bright objects well, COS measures exceedingly faint levels of ultraviolet light emanating from distant cosmic sources, such as quasars in remote galaxies. Working together, the two spectrographs provide a full set of spectroscopic tools for astrophysical research.

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Figure 8: Hubble's STIS captured a spectrum (right) of material ejected by a pair of massive stars called Eta Carinae, while the Wide Field and Planetary Camera 2 took an image of the billowing clouds of gas enveloping the stellar pair (left). The spectrum reveals that one of the lobes contains the elements helium (He), argon (Ar), iron (Fe) and nickel (Ni), image credit: NASA, ESA and the Hubble SM4 ERO Team

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Figure 9: Hubble's 2.4 m diameter primary mirror collects light from its astronomical target and reflex it to a 0.3 m diameter secondary mirror located in the optical tube. This secondary mirror then reflects the light through a hole in the primary mirror to form an image at the telescope’s focal plane. There it is intercepted by pick-off mirrors that pass it into the scientific instruments (image credit: Hubblesite) 9)


Interferometers

Hubble’s interferometers serve a dual purpose — they help the telescope maintain a steady aim and also serve as a scientific instrument. The three interferometers aboard Hubble are called the FGS (Fine Guidance Sensors). The Fine Guidance Sensors measure the relative positions and brightnesses of stars.

When Hubble is pointing at a target, two of the three Fine Guidance Sensors are used to lock the telescope onto the target. For certain observations, the third Fine Guidance Sensor can be used to gather scientific information about a target, such as a celestial object’s angular diameter or star positions that are ten times more accurate than those obtained by ground-based telescopes.

The Fine Guidance Sensors are very sensitive instruments. They seek out stable point sources of light (known as “guide stars”) and then lock onto them to keep the telescope pointing steadily. When a light in the sky is not a point source, the Fine Guidance Sensor cannot lock on and so it rejects the guide star. Often, a rejected guide star is actually a faraway galaxy or a double-star system. Since Hubble was launched in 1990, the Fine Guidance Sensors have detected hundreds of double-star systems that were previously thought to be single stars.


Past Instruments

Only one of the instruments remaining on Hubble — the third Fine Guidance Sensor — was launched with the observatory in 1990. The rest of the instruments were installed during Hubble’s five servicing missions. In addition to installing new instruments, astronauts also repaired two instruments (ACS and STIS) while visiting Hubble on Servicing Mission 4 in 2009. The NICMOS (Near-Infrared Camera and Multi-Object Spectrometer) on Hubble is in hibernation following a cryocooler anomaly, but most of its infrared duties have since been taken over by WFC3.

Hubble’s past instruments include:

• High Speed Photometer

• Faint Object Camera (FOC), provided by ESA

• Faint Object Spectrograph

• Goddard High Resolution Spectrograph

• Wide Field and Planetary Camera

• Wide Field and Planetary Camera 2

• Fine Guidance Sensors (three).


Current Instruments

ACS (Advanced Camera for Surveys) - ACS is a third-generation imaging camera. This camera is optimized to perform surveys or broad imaging campaigns. ACS replaced Hubble's Faint Object Camera (FOC) during Servicing Mission 3B. Its wavelength range extends from the ultraviolet, through the visible and out to the near-infrared (115-1050 nm). ACS has increased Hubble's potential for new discoveries by a factor of ten.

COS (Cosmic Origins Spectrograph) - COS focuses exclusively on ultraviolet (UV) light and is the most sensitive ultraviolet spectrograph ever, increasing the sensitivity at least 10 times in the UV spectrum and up to 70 times when looking at extremely faint objects. It is best at observing points of light, like stars and quasars. COS was installed during during Servicing Mission 4 in May 2009.

STIS (Space Telescope Imaging Spectrograph) - STIS is a second-generation imager/spectrograph. STIS is used to obtain high resolution spectra of resolved objects. STIS has the special ability to simultaneously obtain spectra from many different points along a target. The STIS instrument has a mass of 318 kg and a wavelength range of 115-1000 nm.

STIS spreads out the light gathered by a telescope so that it can be analyzed to determine such properties of celestial objects as chemical composition and abundances, temperature, radial velocity, rotational velocity, and magnetic fields. Its spectrograph can be switched between two different modes of usage:

C So-called "long slit spectroscopy" where spectra of many different points across an object are obtained simultaneously.

1) So-called "echelle spectroscopy" where the spectrum of one object is spread over the detector giving better wavelength resolution in a single exposure.

STIS also has a so-called coronagraph which can block light from bright objects, and in this way enables investigations of nearby fainter objects.

WFC3 (Wide Field Camera 3) - Wide Field Camera 3 is the main imager on the telescope. It has a camera that records visible and ultraviolet (UVIS, 200-1000 nm) wavelengths of light and is 35 times more sensitive in the UV wavelengths than its predecessor. A second camera that is built to view infrared (NIR, 850-1700 nm) light increases Hubble's IR resolution from 65,000 to 1 million pixels. Its combination of field-of-view, sensitivity, and low detector noise results in a 15-20 time improvement over Hubble’s previous IR camera. WFC3 was jointly developed at GSFC, STScI (Space Telescope Science Institute) in Baltimore and Ball Aerospace & Technologies Corporation in Boulder, CO. 10)

FGS (Fine Guidance Sensor) – The FGS provides pointing information for the spacecraft by locking onto guide stars. The FGS can also function as a scientific instrument by precisely measuring the relative positions of stars, detecting rapid changes in a star’s brightness, and resolving double-star systems that appear as point sources even to Hubble’s cameras. Hubble has three FGSs onboard the observatory.

NICMOS (Near Infrared Camera and Multi-Object Spectrometer) – NICMOS has the ability to obtain images and spectroscopic observations of astronomical targets at near-infrared wavelengths. Although NICMOS is currently inactive, most of its functionality is replaced by Hubble’s other science instruments.


Note: As of 25 April 2020, the previously large Hubble file has been split into three files, to make the file handling manageable for all parties concerned, in particular for the user community.

This article covers the Hubble mission and its imagery in the period 2020, in addition to some of the mission milestones.

Hubble status and imagery in the period 2019

Hubble status and imagery in the period 2018-2015 as well as the Hubble Servicing Missions & Ground Segment




HST (Hubble Space Telescope) - Status and some observation imagery in the period 2020

• 31 July 2020: A main-sequence star, like our Sun, is the term applied to a star during the longest period of its life, when it burns fuel steadily. Our Sun’s fuel will run out in approximately 6 billion years, and it will then move on to the next stage of its life when it will turn into a red giant. Astronomers studying NGC 2203, which contains stars that are roughly twice as massive as our Sun, found that rotation rates might be a factor as to why some of the stars stay longer than usual in this main-sequence phase of their life. 11)

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Figure 10: Looking its best ever is the star cluster NGC 2203, here imaged by the NASA/ESA Hubble Space Telescope. Aside from its dazzling good looks, this cluster of stars contains lots of astronomical treats that have helped astronomers puzzle together the lifetimes of stars (image credit: ESA/Hubble & NASA, L. Girardi)

• 24 July, 2020: A notable feature of most spiral galaxies is the multitude of arching spiral arms that seemingly spin out from the galaxy’s center. In this image, taken with the NASA/ESA Hubble Space Telescope, the stunning silvery-blue spiral arms of the galaxy NGC 4848 are observed in immense detail. Not only do we see the inner section of the spiral arms containing hundreds of thousands of young, bright, blue stars, but Hubble has also captured the extremely faint wispy tails of the outer spiral arms. 12) Myriad more distant and delightfully diverse galaxies appear in the background. 13)

- If you are situated in the Northern Hemisphere with a large telescope, you might just be able to observe the ghost-like appearance of this faint galaxy within the faint constellation of Coma Berenices (Berenice’s Hair).

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Figure 11: Hubble snaps a ghostly galaxy. This wispy barred spiral galaxy was first discovered in 1865 by the German astronomer Heinrich Louis d’Arrest. In his career, Heinrich also notably discovered the asteroid 76 Freia and many other galaxies and he also contributed to the discovery of Neptune (image credit: ESA/Hubble & NASA, M. Gregg; CC BY 4.0)

• 23 July 2020: Saturn is truly the lord of the rings in this latest snapshot from NASA's Hubble Space Telescope, taken on July 4, 2020, when the opulent giant world was 839 million miles (1.35 billion km, or 9.5 AU) from Earth. This new Saturn image was taken during summer in the planet's northern hemisphere. 14)

- Hubble found a number of small atmospheric storms. These are transient features that appear to come and go with each yearly Hubble observation. The banding in the northern hemisphere remains pronounced as seen in Hubble's 2019 observations, with several bands slightly changing color from year to year. The ringed planet's atmosphere is mostly hydrogen and helium with traces of ammonia, methane, water vapor, and hydrocarbons that give it a yellowish-brown color.

- Hubble photographed a slight reddish haze over the northern hemisphere in this color composite. This may be due to heating from increased sunlight, which could either change the atmospheric circulation or perhaps remove ices from aerosols in the atmosphere. Another theory is that the increased sunlight in the summer months is changing the amounts of photochemical haze produced. "It's amazing that even over a few years, we're seeing seasonal changes on Saturn," said lead investigator Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Conversely, the just-now-visible south pole has a blue hue, reflecting changes in Saturn's winter hemisphere.

- Hubble's sharp view resolves the finely etched concentric ring structure. The rings are mostly made of pieces of ice, with sizes ranging from tiny grains to giant boulders. Just how and when the rings formed remains one of our solar system's biggest mysteries. Conventional wisdom is that they are as old as the planet, over 4 billion years. But because the rings are so bright – like freshly fallen snow – a competing theory is that they may have formed during the age of the dinosaurs. Many astronomers agree that there is no satisfactory theory that explains how rings could have formed within just the past few hundred million years. "However, NASA's Cassini spacecraft measurements of tiny grains raining into Saturn's atmosphere suggest the rings can only last for 300 million more years, which is one of the arguments for a young age of the ring system," said team member Michael Wong of the University of California, Berkeley.

- Two of Saturn's icy moons are clearly visible in this exposure: Mimas at right, and Enceladus at bottom.

- This image is taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL is helping scientists understand the atmospheric dynamics and evolution of our solar system's gas giant planets. In Saturn's case, astronomers continue tracking shifting weather patterns and storms.

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

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Figure 12: NASA's Hubble Space Telescope captured this image of Saturn on July 4, 2020. Two of Saturn's icy moons are clearly visible in this exposure: Mimas at right, and Enceladus at bottom. This image is taken as part of the Outer Planets Atmospheres Legacy (OPAL) project. OPAL is helping scientists understand the atmospheric dynamics and evolution of our solar system's gas giant planets. In Saturn's case, astronomers continue tracking shifting weather patterns and storms (image credits: NASA, ESA, A. Simon (Goddard Space Flight Center), M.H. Wong (University of California, Berkeley), and the OPAL Team)

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Figure 13: These images are a composite of separate exposures acquired by the WFC3 instrument on the Hubble Space Telescope. Several filters were used to sample narrow wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Blue: F395N Green: F502N Red: F631N (Saturn 2020 compass image)

• 17 July 2020: Galaxies are well known as the birthplaces of stars and planets thanks to the overwhelmingly large amount of dust and gas within them. Over time, cold gas coalesces into molecular clouds, leading to the further emergence of star-forming regions. 15)

- When a massive new star (or stars) starts to shine while still within the cool molecular cloud from which it formed, its energetic radiation can ionize the cloud’s hydrogen and create a large, hot bubble of ionized gas. Amazingly, located within this bubble of hot gas around a nearby massive star are the frEGGs (Free-floating Evaporating Gaseous Globules): dark compact globules of dust and gas, some of which are also giving birth to low-mass stars. The boundary between the cool, dusty frEGG and hot gas bubble is seen as the glowing purple/blue edges in this fascinating image (Figure 14).

- Learning more about these odd objects can help astronomers understand how stars like our Sun form under external influences. In fact, our Sun may have even been born in a frEGG!

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Figure 14: This image taken with the NASA/ESA Hubble Space Telescope depicts a fantastic new class of star-forming nursery, known as frEGGs. This object, known as J025027.7+600849, is located in the constellation of Cassiopeia (image credit: ESA/Hubble & NASA, R. Sahai; CC BY 4.0)

• 17 July 2020: As beautiful as the surrounding space may be, the sparkling galaxy in the foreground of this image from the NASA/ESA Hubble Space Telescope undeniably steals the show. 16)

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Figure 15: This spotlight-hogging galaxy, seen set against a backdrop of more distant galaxies of all shapes and sizes, is known as PGC 29388. Although it dominates in this image, this galaxy is a small player on the cosmic stage and is known as a dwarf elliptical galaxy. As the “dwarf” moniker suggests, the galaxy is on the smaller side, and boasts a “mere” 100 million to a few billion stars — a very small number indeed when compared to the Milky Way's population of around 250 billion to 400 billion stellar residents (image credit: ESA/Hubble & NASA, T. Armandroff)

• 10 July 2020: Hubble image of the week. The sculpted galaxy (NGC 7513) is moving at the astounding speed of 1564 km/s, and it is heading away from us. For context, the Earth orbits the Sun at about 30 km/s. Though NGC 7513’s apparent movement away from the Milky Way might seem strange, it is not that unusual. 17)

- While some galaxies, like the Milky Way and the Andromeda galaxy, are caught in each other’s gravitational pull and will eventually merge together, the vast majority of galaxies in our Universe appear to be moving away from each other. This phenomenon is due to the expansion of the Universe, and it is the space between galaxies that is stretching, rather than the galaxies themselves moving.

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Figure 16: Captured by the NASA/ESA Hubble Space Telescope, this image shows NGC 7513, a barred spiral galaxy. Located approximately 60 million light-years away, NGC 7513 lies within the Sculptor constellation in the southern hemisphere (image credit: ESA/Hubble & NASA, M. Stiavelli; CC BY 4.0)

• 03 July 2020: The spiral pattern shown by the galaxy in this image from the NASA/ESA Hubble Space Telescope is striking because of its delicate, feathery nature. These "flocculent" spiral arms indicate that the recent history of star formation of the galaxy, known as NGC 2775, has been relatively quiet. There is virtually no star formation in the central part of the galaxy, which is dominated by an unusually large and relatively empty galactic bulge, where all the gas was converted into stars long ago. 18)

- Millions of bright, young, blue stars shine in the complex, feather-like spiral arms, interlaced with dark lanes of dust. Complexes of these hot, blue stars are thought to trigger star formation in nearby gas clouds. The overall feather-like spiral patterns of the arms are then formed by shearing of the gas clouds as the galaxy rotates. The spiral nature of flocculents stands in contrast to the grand design spirals, which have prominent, well defined-spiral arms.

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Figure 17: NGC 2275 is classified as a flocculent spiral galaxy, located 67 million light-years away in the constellation of Cancer [image credit: ESA/Hubble & NASA, J. Lee and the PHANGS-HST Team; CC BY 4.0; Acknowledgement: Judy Schmidt (Geckzilla)]

• 30 June, 2020: At first sight, this image from the NASA/ESA Hubble Space Telescope portrays the sparkling stars of AGC111977, a dwarf galaxy located around 15 million light years away and visible in the lower left part of the image. Other galaxies appear sprinkled across the frame, along with foreground stars from our own galaxy, the Milky Way. 19)

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Figure 18: After closer inspection, something else comes to sight, much closer to home. Towards the lower right corner of the frame, two elongated streaks are faintly visible: the trails of asteroids – small rocky bodies in our Solar System – crossing their ways in the foreground of the stars and galaxies that Hubble was observing [image credit: ESA/Hubble & NASA; J. Cannon (Macalester College)]

- The image combines observations obtained on 16 November 2012 with Hubble’s ACS (Advanced Camera for Surveys) instrument using two different filters (606 nm, shown in blue, and 814 nm, shown in red). As the asteroids moved relative to Hubble during the observation, both trails have been imaged subsequently in each filter and thus appear part red and part blue.

- The two asteroids are located at different distances from us, so they did not actually collide as their intersecting streaks might suggest. They were uncovered by citizen scientists Sovan Acharya, Graeme Aitken, Claude Cornen, Abe Hoekstra and Edmund Perozzi, some of the volunteers who have been inspecting images from the iconic space telescope in search for rocky interlopers as part of the Hubble Asteroid Hunter citizen science project.

- Launched one year ago, on International Asteroid Day 2019, the Hubble Asteroid Hunter is a collaboration between ESA and the Zooniverse, inviting members of the public to identify asteroids that had been serendipitously observed by the Hubble Space Telescope. Since then, 9000 volunteers from all over the world provided 2 million classifications of 140 000 composite Hubble images, finding 1500 asteroid trails – about one every hundred images.

- In the project’s first phase, volunteers could explore a collection of archival Hubble images where calculations by the Solar System Objects pipeline of ESASky, ESA's discovery portal for astronomy, indicated that an asteroid might have been crossing the space telescope’s field of view at the time of the observations. The sheer number and enthusiasm of volunteers led the team to expand the project, including more images of the sky collected by Hubble over the years.

- Besides asteroids, the volunteers have also identified trails left by satellites in orbits higher than Hubble’s, intriguing instances of gravitational lensing, and ring-shaped features that arise when galaxies collide.

- The project experienced a surge in participation during the past few months, as many people around the world were staying at home due to the COVID-19 pandemic, leading to a threefold increase in the number of classifications. Thanks to the continued efforts of the volunteers, this citizen science project is now nearing completion, with only the infrared images left to explore.

- Meanwhile, the team is working to identify the asteroids that were uncovered as part of the project – including the two pictured in this image – to possibly match them with known asteroids in the Minor Planet Center database, and calculate their distances from us. Stay tuned!

- Asteroid Day is a UN-endorsed awareness campaign day to mark the anniversary of the 30 June 1908 Tunguska impact, and this year ESA is taking part in Asteroid Day TV distributed by the Luxembourg-based Asteroid Foundation. To watch programming by ESA as well as top content makers including Discovery Science, TED, IMAX, BBC, CNN, ESO and other educational producers, access https://asteroidday.org/

• 26 June 2020: The galaxy known as NGC 5907 stretches wide across this image. Appearing as an elongated line of stars and dark dust, the galaxy is categorized as a spiral galaxy just like our own Milky Way. In this new image from the NASA/ESA Hubble Space Telescope, we don’t see the beautiful spiral arms because we are viewing it edge-on, like looking at the rim of a plate. It is for this reason that NGC 5907 is also known as the Knife Edge Galaxy. 20)

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Figure 19: The Knife Edge Galaxy is about 50 million light-years from Earth, lying in the northern constellation of Draco. Although not visible in this image, ghostly streams of stars on large arching loops extend into space, circling around the galaxy; they are believed to be remnants of a small dwarf galaxy, torn apart by the Knife Edge Galaxy and merged with it over four billion years ago [image credit: ESA/Hubble & NASA, R. de Jong; CC BY 4.0; Acknowledgement: Judy Schmidt (Geckzilla)]

• 18 June 2020: The NASA/ESA Hubble Space Telescope demonstrates its full range of imaging capabilities with two new images of planetary nebulae. The images depict two nearby young planetary nebulae, NGC 6302, dubbed the Butterfly Nebula, and NGC 7027. Both are among the dustiest planetary nebulae known and both contain unusually large masses of gas, which made them an interesting pair for study in parallel by a team of researchers. 21)

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Figure 20: These two new images from the Hubble Space Telescope depict two nearby young planetary nebulae, NGC 6302, dubbed the Butterfly Nebula, and NGC 7027, which resembles a jewel bug. Both are among the dustiest planetary nebulae known and both contain unusually large masses of gas [image credit: NASA, ESA, and J. Kastner (RIT)]

- As nuclear fusion engines, most stars live placid lives for hundreds of millions to billions of years. But near the end of their lives they can turn into crazy whirligigs, puffing off shells and jets of hot gas. Astronomers have used Hubble to dissect such crazy fireworks happening in these two planetary nebulae. The researchers have found unprecedented levels of complexity and rapid changes in the jets and gas bubbles blasting off of the stars at the center of each nebula. 22) Hubble is now allowing the researchers to converge on an understanding of the mechanisms underlying this chaos.

- The Hubble Space Telescope has imaged these objects before, but not for many years and never before with the Wide Field Camera 3 instrument across its full wavelength range — making observations in near-ultraviolet to near-infrared light. “These new multi-wavelength Hubble observations provide the most comprehensive view to date of both of these spectacular nebulae,” said Joel Kastner of the Rochester Institute of Technology, Rochester, New York, leader of the new study. “As I was downloading the resulting images, I felt like a kid in a candy store.”

- The new Hubble images reveal in vivid detail how both nebulae are splitting themselves apart on extremely short timescales — allowing astronomers to see changes over the past couple of decades. In particular, Hubble’s broad multi-wavelength views of each nebula are helping the researchers to trace the histories of shock waves in them. Such shocks are typically generated when fresh, fast stellar winds slam into and sweep up more slowly expanding gas and dust ejected by the star in its recent past, generating bubble-like cavities with well-defined walls.

- Researchers suspect that at the heart of each nebula were two stars orbiting around each other. Evidence for such a central “dynamic duo” comes from the bizarre shapes of these nebulas. Each has a pinched, dusty waist and polar lobes or outflows, as well as other, more complex symmetrical patterns.

- A leading theory for the generation of such structures in planetary nebulae is that the mass-losing star is one of two stars in a binary system. The two stars orbit one another closely enough that they eventually interact, producing a gas disc around one or both stars. The disc then launches jets that inflate polar-directed lobes of outflowing gas.

- Another, related, popular hypothesis is that the smaller star of the pair may merge with its bloated, more rapidly evolving stellar companion. This very short-lived “common envelope” binary star configuration can also generate wobbling jets, forming the trademark bipolar outflows commonly seen in planetary nebulae. However, the suspect companion stars in these planetary nebulae have not been directly observed. Researchers suggest this may be because these companions are next to, or have already been swallowed by, far larger and brighter red giant stars.

- NGC 6302, commonly known as the Butterfly Nebula, exhibits a distinct S-shaped pattern seen in reddish-orange in the image. Imagine a lawn sprinkler spinning wildly, throwing out two S-shaped streams. In this case it is not water in the air, but gas blown out at high speed by a star. And the “S” only appears when captured by the Hubble camera filter that records near-infrared emission from singly ionized iron atoms. This iron emission is indicative of energetic collisions between both slow and fast winds, which is most commonly observed in active galactic nuclei and supernova remnants.

- "This is very rarely seen in planetary nebulae,” explained team member Bruce Balick of the University of Washington in Seattle. “Importantly, the iron emission image shows that fast, off-axis winds penetrate far into the nebula like tsunamis, obliterating former clumps in their paths and leaving only long tails of debris.”

- The accompanying image of NGC 7027, which resembles a jewel bug, indicates that it had been slowly puffing away its mass in quiet, spherically symmetric or perhaps spiral patterns for centuries — until relatively recently. “Something recently went haywire at the very center, producing a new cloverleaf pattern, with bullets of material shooting out in specific directions,” Kastner explained.

• 05 June 2020: Almost like snowflakes, the stars of the globular cluster NGC 6441 sparkle peacefully in the night sky, about 13,000 light-years from the Milky Way’s galactic center. Like snowflakes, the exact number of stars in such a cluster is difficult to discern. It is estimated that together the stars weigh 1.6 million times the mass of the Sun, making NGC 6441 one of the most massive and luminous globular clusters in the Milky Way. 23)

- NGC 6441 is host to four pulsars that each complete a single rotation in a few milliseconds. Also hidden within this cluster is JaFu 2, a planetary nebula. Despite its name, this has little to do with planets. A phase in the evolution of intermediate-mass stars, planetary nebulae last for only a few tens of thousands of years, the blink of an eye on astronomical timescales.

- There are about 150 known globular clusters in the Milky Way. Globular clusters contain some of the first stars to be produced in a galaxy, but the details of their origins and evolution still elude astronomers.

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Figure 21: Hubble image of the week: snowflakes (image credit: ESA/Hubble & NASA, G. Piotto)

• 03 June 2020: New results from the NASA/ESA Hubble Space Telescope suggest the formation of the first stars and galaxies in the early universe took place sooner than previously thought. A European team of astronomers have found no evidence of the first generation of stars, known as Population III stars, as far back as when the universe was just 500 million years old. 24) 25)

- The exploration of the very first galaxies remains a significant challenge in modern astronomy. We do not know when or how the first stars and galaxies in the universe formed. These questions can be addressed with the Hubble Space Telescope through deep imaging observations. Hubble allows astronomers to view the universe back to within 500 million years of the big bang.

- A team of European researchers, led by Rachana Bhatawdekar of the European Space Agency, set out to study the first generation of stars in the early Universe. Known as Population III stars [1], these stars were forged from the primordial material that emerged from the Big Bang. Population III stars must have been made solely out of hydrogen, helium and lithium, the only elements that existed before processes in the cores of these stars could create heavier elements, such as oxygen, nitrogen, carbon and iron.

- Bhatawdekar and her team probed the early Universe from about 500 million to 1 billion years after the Big Bang by studying the cluster MACSJ0416 and its parallel field with the Hubble Space Telescope [with supporting data from NASA's Spitzer Space Telescope and the ground-based VLT (Very Large Telescope) of the European Southern Observatory]. "We found no evidence of these first-generation Population III stars in this cosmic time interval" said Bhatawdekar of the new results.

- The result was achieved using the Hubble's Space Telescope's Wide Field Camera 3 and Advanced Camera for Surveys [2], as part of the Hubble Frontier Fields program. This program (which observed six distant galaxy clusters from 2012 to 2017) produced the deepest observations ever made of galaxy clusters and the galaxies located behind them which were magnified by the gravitational lensing effect, thereby revealing galaxies 10 to 100 times fainter than any previously observed. The masses of foreground galaxy clusters are large enough to bend and magnify the light from the more distant objects behind them. This allows Hubble to use these cosmic magnifying glasses to study objects that are beyond its nominal operational capabilities.

- Bhatawdekar and her team developed a new technique that removes the light from the bright foreground galaxies that constitute these gravitational lenses. This allowed them to discover galaxies with lower masses than ever previously observed with Hubble, at a distance corresponding to when the Universe was less than a billion years old. At this point in cosmic time, the lack of evidence for exotic stellar populations and the identification of many low-mass galaxies supports the suggestion that these galaxies are the most likely candidates for the re-ionization of the Universe. This period of re-ionization in the early Universe is when the neutral intergalactic medium was ionized by the first stars and galaxies.

- "These results have profound astrophysical consequences as they show that galaxies must have formed much earlier than we thought," said Bhatawdekar. "This also strongly supports the idea that low-mass/faint galaxies in the early Universe are responsible for re-ionization."

- These results [3] also suggest that the earliest formation of stars and galaxies occurred much earlier than can be probed with the Hubble Space Telescope. This leaves an exciting area of further research for the upcoming NASA/ESA/CSA James Webb Space Telescope – to study the Universe's earliest galaxies.

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Figure 22: Artist's impression of the early Universe (image credit: ESA/Hubble, M. Kornmesser, CC BY 4.0)

Notes

[1] The name Population III arose because astronomers had already classified the stars of the Milky Way as Population I (stars like the Sun, which are rich in heavier elements) and Population II (older stars with a low heavy-element content, found in the Milky Way bulge and halo, and in globular star clusters).

[2] Owing to the expansion of the Universe, the light from the distant galaxies is shifted from ultraviolet and optical wavelengths into the infrared part of the electromagnetic spectrum. Hubble's Wide Field Camera 3 is well equipped to probe this part of the spectrum. In addition, the telescope's Advanced Camera for Surveys is optimized for visible/ light observations.

[3] These results are based on a previous 2019 paper by Bhatawdekar et al., and a paper that will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society (MNRAS). These results are also being presented at a press conference during the 236th meeting of the American Astronomical Society on 3 June 2020.

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Figure 23: This image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J0416. This is one of six being studied by the Hubble Frontier Fields program, which together have produced the deepest images of gravitational lensing ever made. Scientists used intracluster light (visible in blue) to study the distribution of dark matter within the cluster [image credit: NASA, ESA, and M. Montes (University of New South Wales, Sydney, Australia)]

• 29 May 2020: Far away in the Ursa Major constellation is a swirling galaxy that would not look out of place on a coffee made by a starry-eyed barista. NGC 3895 is a barred spiral galaxy that was first spotted by William Herschel in 1790 and was later observed by the NASA/ESA Hubble Space Telescope. 26)

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Figure 24: Hubble's orbit high above the Earth's distorting atmosphere allows astronomers to make the very high resolution observations that are essential to opening new windows on planets, stars and galaxies — such as this beautiful view of NGC 3895. The telescope is positioned approximately 570 km above the ground, where it whirls around Earth at 28,000 km/hr and takes 96 minutes to complete one orbit (image credit: ESA/Hubble, NASA, and R. Barrows; CC BY 4.0)

• 28 May 2020: The NASA/ESA Hubble Space Telescope was used to conduct a three-year study of the crowded, massive and young star cluster Westerlund 2. The research found that the material encircling stars near the cluster’s center is mysteriously devoid of the large, dense clouds of dust that would be expected to become planets in a few million years. Their absence is caused by the cluster’s most massive and brightest stars that erode and disperse the discs of gas and dust of neighboring stars. This is the first time that astronomers have analyzed an extremely dense star cluster to study which environments are favorable to planet formation. 27)

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Figure 25: The star cluster Westerlund 2 (Milky Way). This image shows the sparkling centerpiece of Hubble's 25th anniversary tribute. Westerlund 2 is a giant cluster of about 3000 stars located 20,000 light-years away in the constellation Carina. Hubble's near-infrared imaging camera pierces through the dusty veil enshrouding the stellar nursery, giving astronomers a clear view of the dense concentration of stars in the central cluster (image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team)

The Westerlund 2 star cluster's raucous core is no place to form planets 28)

- Astronomers using NASA's Hubble Space Telescope are finding that planets have a tough time forming in the rough-and-tumble central region of the massive, crowded star cluster Westerlund 2. Located 20,000 light-years away, Westerlund 2 is a unique laboratory to study stellar evolutionary processes because it's relatively nearby, quite young, and contains a large stellar population.

- A three-year Hubble study of stars in Westerlund 2 revealed that the precursors to planet-forming disks encircling stars near the cluster's center are mysteriously devoid of large, dense clouds of dust that in a few million years could become planets.

- However, the observations show that stars on the cluster's periphery do have the immense planet-forming dust clouds embedded in their disks. Researchers think our solar system followed this recipe when it formed 4.6 billion years ago.

- So why do some stars in Westerlund 2 have a difficult time forming planets while others do not? It seems that planet formation depends on location, location, location. The most massive and brightest stars in the cluster congregate in the core, which is verified by observations of other star-forming regions. The cluster's center contains at least 30 extremely massive stars, some weighing up to 80 times the mass of the Sun. Their blistering ultraviolet radiation and hurricane-like stellar winds of charged particles blowtorch disks around neighboring lower-mass stars, dispersing the giant dust clouds.

- "Basically, if you have monster stars, their energy is going to alter the properties of the disks around nearby, less massive stars," explained Elena Sabbi, of the Space Telescope Science Institute in Baltimore, Maryland, lead researcher of the Hubble study. "You may still have a disk, but the stars change the composition of the dust in the disks, so it's harder to create stable structures that will eventually lead to planets. We think the dust either evaporates away in 1 million years, or it changes in composition and size so dramatically that planets don't have the building blocks to form."

- The Hubble observations represent the first time that astronomers analyzed an extremely dense star cluster to study which environments are favorable to planet formation. Scientists, however, are still debating whether bulky stars are born in the center or whether they migrate there. Westerlund 2 already has massive stars in its core, even though it is a comparatively young 2-million-year-old system.

- Using Hubble's Wide Field Camera 3, the researchers found that of the nearly 5,000 stars in Westerlund 2 with masses between 0.1 to 5 times the Sun's mass, 1,500 of them show fluctuations in their light as the stars accrete material from their disks. Orbiting material clumped within the disk would temporarily block some of the starlight, causing brightness fluctuations.

- However, Hubble detected the signature of such orbiting material only around stars outside the cluster's packed central region. The telescope witnessed large drops in brightness for as much as 10 to 20 days around 5% of the stars before they returned to normal brightness. They did not detect these dips in brightness in stars residing within four light-years of the center. These fluctuations could be caused by large clumps of dust passing in front of the star. The clumps would be in a disk tilted nearly edge-on to the view from Earth. "We think they are planetesimals or structures in formation," Sabbi explained. "These could be the seeds that eventually lead to planets in more evolved systems. These are the systems we don't see close to very massive stars. We see them only in systems outside the center."

- Thanks to Hubble, astronomers can now see how stars are accreting in environments that are like the early universe, where clusters were dominated by monster stars. So far, the best known nearby stellar environment that contains massive stars is the starbirth region in the Orion Nebula. However, Westerlund 2 is a richer target because of its larger stellar population.

- "Hubble's observations of Westerlund 2 give us a much better sense of how stars of different masses change over time, and how powerful winds and radiation from very massive stars affect nearby lower-mass stars and their disks," Sabbi said. "We see, for example, that lower-mass stars, like our Sun, that are near extremely massive stars in the cluster still have disks and still can accrete material as they grow. But the structure of their disks (and thus their planet-forming capability) seems to be very different from that of disks around stars forming in a calmer environment farther away from the cluster core. This information is important for building models of planet formation and stellar evolution."

- This cluster will be an excellent laboratory for follow-up observations with NASA's upcoming James Webb Space Telescope, an infrared observatory. Hubble has helped astronomers identify the stars that have possible planetary structures. With Webb, researchers can study which disks around stars are not accreting material and which disks still have material that could build up into planets. This information on 1,500 stars will allow astronomers to map a path on how star systems grow and evolve. Webb also can study the chemistry of the disks in different evolutionary phases and watch how they change, and help astronomers determine what influence environment plays in their evolution.

- NASA's planned infrared observatory, the Nancy Grace Roman Space Telescope, will be able to perform Sabbi's study on a much larger area. Westerlund 2 is just a small slice of an immense star-formation region. These vast regions contain clusters of stars with different ages and different densities. Astronomers could use Roman Space Telescope observations to start to build up statistics on how a star's characteristics, like its mass or outflows, affect its own evolution or the nature of stars that form nearby. The observations could also provide more information on how planets form in tough environments. 29)

• 22 May 2020: Unlike a spiral or elliptical galaxy, the galaxy KK 246 looks like glitter spilled across a black velvet sheet. KK 246, also known as ESO 461-036, is a dwarf irregular galaxy residing within the Local Void, a vast region of empty space. This lonely galaxy is the only one known for certain to reside in this enormous volume, along with 15 others that have been tentatively identified. 30)

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Figure 26: Although the picture appears to be full of galaxies, they are actually beyond this void, and instead form part of other galaxy groups or clusters. Cosmic voids, such as this one, are the spaces within the web-like structure of the Universe wherein very few or no galaxies exist. Adjacent to the Local Group, this region of empty space is at least 150 million light-years across. For perspective, our own Milky Way galaxy is estimated to be 150,000 light-years across, making this void immense in its nothingness (image credit: ESA/Hubble & NASA, E. Shaya, L. Rizzi, B. Tully, et al.; CC BY 4.0)

• 20 May 2020: Today, NASA announced that it is naming its next-generation space telescope, the Wide Field Infrared Survey Telescope (WFIRST), in honor of Dr. Nancy Grace Roman, NASA’s first Chief Astronomer, who paved the way for space telescopes focused on the broader universe. The newly named Nancy Grace Roman Space Telescope (or Roman Space Telescope, for short), is set to launch in the mid-2020s. 31)

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Figure 27: An artist's illustration of the Roman Space Telescope against a starry background, formerly WFIRST. It will revolutionize astronomy by building on the science discoveries and technological leaps of the Hubble and James Webb space telescopes (image credit: NASA/GSFC)

- Dr. Roman is credited with making the Hubble Space Telescope a reality, leading to her nickname "mother of Hubble." In the mid-1960s, she set up a committee of astronomers and engineers to envision a telescope that could accomplish important scientific goals. She convinced NASA and Congress that it was a priority to launch the most powerful space telescope the world had ever seen. She argued that, for the price of a movie ticket, each American could be given years of scientific discoveries.

- Her vision was realized when Hubble launched in 1990. Hubble turned out to be the most scientifically revolutionary space telescope of all time.

- The Space Telescope Science Institute (STScI) in Baltimore, Maryland, is the science operations center for Hubble, and will house the science and mission operations centers for the upcoming James Webb Space Telescope. In 2019, NASA announced that STScI would serve as the science operations center for the Roman Space Telescope. In that role, the Institute will plan, schedule, and carry out observations, process and archive mission datasets, and engage and inform the astronomical community and the public.

• 08 May 2020: Galaxy Galaxy, Burning Bright! Hubble Spots Source of Two Brilliant Supernovae. 32)

- There are a few different ways that supernova can form. In the case of these two supernovae, the explosions evolved from two independent binary star systems in which the stellar remnant of a Sun-like star, known as a white dwarf, was collecting material from its companion star. Feeding off of its partner, the white dwarf gorged on the material until it reached a maximum mass. At this point, the star collapsed inward before exploding outward in a brilliant supernova.

- Two of these events were spotted in NGC 3583, and though not visible in this picture of the week, we can still marvel at the galaxy’s fearful symmetry.

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Figure 28: In the forests of the night lies a barred spiral galaxy called NGC 3583, imaged here by the NASA/ESA Hubble Space Telescope. This is a barred spiral galaxy with two arms that twist out into the Universe. This galaxy is located 98 million light-years away from the Milky Way. Two supernovae exploded in this galaxy, one in 1975 and another, more recently, in 2015 (image credit: ESA/Hubble & NASA, A. Riess et al.; CC BY 4.0)

• 01 May 2020: This sparkling spiral galaxy looks almost stretched across the sky in this new image from the NASA/ESA Hubble Space Telescope. Known as NGC 4100, the galaxy boasts a neat spiral structure and swirling arms speckled with the bright blue hue of newly formed stars. 33)

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Figure 29: Like so many of the stunning images of galaxies we enjoy today, this image was captured by Hubble’s Advanced Camera for Surveys (ACS). This remarkable instrument was installed in 2002, and, with some servicing over the years by intrepid astronauts, is still going strong. You can access many of the stunning images captured by the ACS here, featuring objects from out-of-this-world spiral galaxies to dark, imposing nebulae, bizarre cosmic phenomena, and sparkling clusters made up of thousands upon thousands of stars (image credit: ESA/Hubble & NASA, L. Ho; CC BY 4.0)

• 30 April 2020: During its 30 years in orbit around Earth, the NASA/ESA Hubble Space Telescope has witnessed the changing nature of spaceflight as the skies have filled with greater numbers of satellites, the International Space Station was born and in-space crashes and explosions have created clouds of fast-moving space debris. 34)

- Hubble itself has felt the impact of this debris, accumulating tiny impact craters across its solar panels that evidence a long and eventful life in space. So what can we learn from these impacts, and what does the future hold for Hubble?

- In 1993, the first Shuttle mission to ‘spruce up’ Hubble was conducted. By providing the space observatory with corrective optics, it was suddenly able to take the incredibly sharp images of the Universe loved by the world over.

- While the astronauts were there, they replaced the observatory’s solar arrays which had been ‘jittering’ due to temperature fluctuations. One of the panels was disposed of in orbit, later burning up in Earth’s atmosphere, but the other was brought back down to Earth.

- Part of ESA’s contribution to Hubble was to design, manufacture and provide its solar arrays in exchange for observation time, meaning the returned array was available for the Agency to inspect.

- This was one of the earliest opportunities in the history of space exploration to see the impact of more than two years in space on an orbiting satellite. The team discovered hundreds of impact craters pocketing the surface of just a small section of the solar array, ranging from µm to millimeters in diameter.

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Figure 30: Astronaut Kathy Thornton threw the damaged Hubble array into free space once it became clear its failed compensation mechanism had bent it into a bow-like shape, making refurling for return to Earth at the end of STS-61 on Servicing Mission in December 1993 impossible (image credit: NASA)

- Nine years later, the solar panels were again replaced and returned to Earth this time having accumulated almost a decade of impact craters.

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Figure 31: Hubble solar cell impact damage. Post-flight analysis of an impact crater on one of the solar wings deployed by the Space Shuttle Endeavour in 1993 and retrieved by Space Shuttle Columbia in 2002 (image credit: ESA)

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Figure 32: ESA built-solar cells retrieved from the Hubble Space Telescope in 2002. Solar cells in space undergo various kinds of degradation over time – meteorite impacts being the single most violent. Note two front impacts and one from the rear side seen on bottom right (image credit: ESA)

- This array is now on display at ESA’s Technology Center (ESTEC) in The Netherlands, but a tiny piece came to the ESOC mission control in Germany, home to the Space Debris Office.

Array of evidence of Hubble’s early bombardment

- Although we don't know exactly when each impact crater was formed, they must have occurred during the solar array’s period in orbit. As such, imprinted on them, is unique evidence of spaceflight activity during their time in space.

- The impact craters were studied to determine their size and depth, but also to seek out potential new residues. Given that the chemical composition of the solar cell was known, ‘alien’ materials or elements could have been brought into the crater by the impactor.

- Metals like iron and nickel would suggest an impact from a natural source – fragments of asteroids and comets known as micrometeoroids. The craters found in Hubble’s solar arrays however contained small amounts of aluminum and oxygen, a strong indication of human activity in the form of ‘solid rocket motor’ firing residues.

- The space debris team, as part of a larger effort with partners in industry and academia, were able to match the shape and size of these craters to models of rocket firings that were known to have happened at the time, finding a match between craters observed and craters expected.

Was Hubble hurt?

- These tiny particles, ranging from micrometers up to a millimeter in size, would have struck Hubble at huge relative speeds of 10 km/s, however they didn't have a major impact on the craft which continues to take incredible images of our Universe.

- Such impacts occur quite frequently for all satellites, the main effect being a continuous but gradual degradation in the amount of power the solar arrays can produce.

- New missions make use of a model created by the space debris team, based on early Hubble impact data, to predict how many impacts can be expected for each mission and what effect this will have on solar power.

Hubble still lives with the threat of collision

- Imagine the Hubble spacecraft in orbit, residing inside a 1 km x 1 km x 1km cube. On average, at any moment, a single piece of µm-sized debris shares that cube with Hubble, because for every cubic kilometer of space around Earth, there is about one tiny debris object.

- This doesn't sound like a lot, but Hubble itself is travelling at 7.6 km/s relative to Earth and so are these tiny fragments of debris. A large fraction of collisions between the two don't happen head on, but at an angle, leading to relative impact speeds of about 10 km/s.

- For simplicity, imagine these particles are travelling at 10 km/s relative to a still Hubble. This is the same as ten of these fast-moving objects crossing in and out of Hubble’s cubic space every second. Because Hubble’s solar panels take up a large surface area, measuring approximately 7 x 2 m, they are more likely to come face-to-face with large numbers of these projectiles.

Figure 33: This animation shows different types of space debris objects and different debris sizes in orbit around Earth. For debris objects bigger than 10 cm the data come from the US Space Surveillance Catalog. (video credit: ESA)

- Hubble today faces a similar threat from small debris fragments as it did soon after it was launched. While µm-sized particles are still being created today, the atmosphere at this low altitude, 547 km above Earth’s surface, also sweeps a number of them away.

- However, the risk from larger objects is unfortunately also increasing. Debris fragments ranging from about 1-10 cm in size are too small to be catalogued and tracked from ground, but have enough energy to destroy an entire satellite. At Hubble's altitude, the probability of a collision with one of these objects has doubled since the early 2000s, from a 0.15% chance per year to a 0.3% today.

Hubble lives where mega-constellations plan to reside

- Some satellites are launched today without the capability to change their orbit. Instead of maneuvering at the end of their life, they can be inserted into relatively low altitudes so that over time Earth’s atmosphere pulls them down to burn up, including the region that Hubble calls home.

- In addition, the total number of operational satellites being put into this region looks set to soon rapidly increase. Some broadband internet constellations, the largest of which are planned to contain thousands of satellites, have their sights set on these heights.

Space Safety at ESA

- To help prevent the build-up of new debris through collisions, ESA's Space Safety program is developing ‘automated collision avoidance’ technologies that will make the process of avoiding collisions more efficient, by automating the decision processes on the ground.

- But what about the debris that’s already out there? In a world first, ESA has commissioned an active debris removal mission that will safely dispose of an item of debris currently in orbit. The ClearSpace-1 mission will target a 100 kg Vespa rocket part, left in orbit after the second flight of ESA’s Vega launcher back in 2013.

- With a mass of 100 kg, the Vespa is close in size to a small satellite. Its relatively simple shape and sturdy construction make it a suitable first goal, before progressing to larger, more challenging captures by follow-up missions – eventually including multi-object capture.

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Figure 34: This image shows the results of a lab test impact between a small sphere of aluminum travelling at approximately 6.8 km per sec and a block of aluminum 18 cm thick. This test simulates what can happen when a small space debris object hits a spacecraft. - In such an impact, the pressure and temperature can exceed those found at the center of the Earth e.g. greater than 365 GPa and more than 6,000 K (image credit: ESA) 35)

• 28 April 2020: These two Hubble Space Telescope images of comet C/2019 Y4 (ATLAS), taken on April 20 and 23, 2020, provide the sharpest views yet of the breakup of the fragile comet. 36) 37)

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Figure 35: These two Hubble Space Telescope images of comet C/2019 Y4 (ATLAS), taken on April 20 (left) and April 23, 2020, provide the sharpest views yet of the breakup of the solid nucleus of the comet. Hubble's eagle-eye view identifies as many as 30 separate fragments. Hubble distinguishes pieces that are roughly the size of a house. Before the breakup, the entire nucleus of the comet may have been the length of one or two football fields. Astronomers aren't sure why this comet broke apart. The comet was approximately 91 million miles (146 million kilometers) from Earth when the images were taken [image credit: NASA, ESA, STScI and D. Jewitt (UCLA)]

- Hubble identified about 30 fragments on April 20, and 25 pieces on April 23. They are all enveloped in a sunlight-swept tail of cometary dust. "Their appearance changes substantially between the two days, so much so that it's quite difficult to connect the dots," said David Jewitt, professor of planetary science and astronomy at UCLA, Los Angeles, and leader of one of two teams that photographed the doomed comet with Hubble. "I don't know whether this is because the individual pieces are flashing on and off as they reflect sunlight, acting like twinkling lights on a Christmas tree, or because different fragments appear on different days."

- "This is really exciting — both because such events are super cool to watch and because they do not happen very often. Most comets that fragment are too dim to see. Events at such scale only happen once or twice a decade," said the leader of a second Hubble observing team, Quanzhi Ye, of the University of Maryland, College Park.

- The results are evidence that comet fragmentation is actually fairly common, say researchers. It might even be the dominant mechanism by which the solid, icy nuclei of comets die. Because this happens quickly and unpredictably, astronomers remain largely uncertain about the cause of fragmentation. Hubble's crisp images may yield new clues to the breakup. Hubble distinguishes pieces as small as the size of a house. Before the breakup, the entire nucleus may have been no more than the length of two football fields.

- One idea is that the original nucleus spun itself into pieces because of the jet action of outgassing from sublimating ices. Because such venting is probably not evenly dispersed across the comet, it enhances the breakup. "Further analysis of the Hubble data might be able to show whether or not this mechanism is responsible," said Jewitt. "Regardless, it's quite special to get a look with Hubble at this dying comet."

- The comet was discovered on Dec. 29, 2019, by the ATLAS (Asteroid Terrestrial-impact Last Alert System) robotic astronomical survey system based in Hawaii. This NASA-supported survey project for Planetary Defense operates two autonomous telescopes that look for Earth-approaching comets and asteroids.

- The comet brightened quickly until mid-March, and some astronomers anticipated that it might be visible to the naked eye in May to become one of the most spectacular comets seen in the last 20 years.

- However, the comet abruptly started to get dimmer instead of brighter. Astronomers speculated that the icy core may be fragmenting, or even disintegrating. ATLAS' fragmentation was confirmed by amateur astronomer Jose de Queiroz, who was able to photograph around three pieces of the comet on 11 April.

- The disintegrating comet was approximately 91 million miles (146 million km) from Earth when the latest Hubble observations were taken. If any of it survives, the comet will make its closest approach to Earth on May 23 at a distance of about 72 million miles (116 million km), and eight days later it will skirt past the Sun at 25 million miles (40 million km).

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

24 April 2020: NASA is celebrating the Hubble Space Telescope's 30 years of unlocking the beauty and mystery of space by unveiling a stunning new portrait of a firestorm of starbirth in a neighboring galaxy. Thirty years ago, on 24 April 1990, Hubble was carried aloft from NASA's Kennedy Space Center in Florida aboard the space shuttle Discovery, along with a five-astronaut crew. Deployed into Earth orbit a day later, the telescope opened a new eye onto the cosmos that has been transformative for our civilization. 38)

- "Hubble has given us stunning insights about the universe, from nearby planets to the farthest galaxies we have seen so far," said Thomas Zurbuchen, associate administrator for science at NASA Headquarters in Washington, D.C. "It was revolutionary to launch such a large telescope 30 years ago, and this astronomy powerhouse is still delivering revolutionary science today. Its spectacular images have captured the imagination for decades, and will continue to inspire humanity for years to come."

- The NASA/ESA Hubble Space Telescope’s iconic images and scientific breakthroughs have redefined our view of the Universe. To commemorate three decades of scientific discoveries, this image is one of the most photogenic examples of the many turbulent stellar nurseries the telescope has observed during its 30-year lifetime. 39)

- The portrait features the giant nebula NGC 2014 and its neighbor NGC 2020 which together form part of a vast star-forming region in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, approximately 163,000 light-years away. The image is nicknamed the ‘Cosmic Reef’ because it resembles an undersea world.

- On 24 April 1990, the Hubble Space Telescope was launched on the Space Shuttle Discovery, along with a five-astronaut crew. Deployed into low Earth orbit a day later, the telescope has since opened our eyes to the cosmos and transformed our collective knowledge of the Universe.

- Hubble has revolutionized modern astronomy not only for astronomers, but also for the public, taking them on a journey of exploration and discovery. Unlike any other telescope before it, Hubble has made astronomy relevant, engaging and accessible for people of all ages.

- The mission has yielded to date 1.4 million observations and provided data that astronomers around the world have used to write more than 17 000 peer-reviewed scientific publications, making it one of the most prolific space observatories in history. Its rich data archive alone will fuel future astronomy research for generations to come.

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Figure 36: Hubble Space Telescope’s iconic images and scientific breakthroughs have redefined our view of the Universe. To commemorate three decades of scientific discoveries, this image is one of the most photogenic examples of the many turbulent stellar nurseries the telescope has observed during its 30-year lifetime. The portrait features the giant nebula NGC 2014 and its neighbor NGC 2020 which together form part of a vast star-forming region in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, approximately 163 000 light-years away. The image is nicknamed the “Cosmic Reef” because it resembles an undersea world (image credit: NASA, ESA, and STScI; CC BY 4.0)

- Each year, Hubble has a small portion of its precious observing time dedicated to taking a special anniversary image, showcasing particularly beautiful and meaningful objects. These observations continue to challenge scientists with surprising new findings and to fascinate the public with ever more evocative images.

Figure 37: Hubble’s collection of anniversary images: To celebrate Hubble’s 30th anniversary, let’s look back at the beauty and science behind each of the anniversary images unveiled as of 2005. In this video, we will also feature the very special 2020 Hubble Space Telescope 30th anniversary image [video credit: ESA/Hubble, Directed by: Bethany Downer; Visual design and editing: Martin Kornmesser; Written by: Bethany Downer; Narration: Sara Mendes da Costa; Images & Videos: NASA, ESA, M. Kornmesser, L. Calçada, ESO, NAOJ, G. Bacon, L. Frattare, Z. Levay and F. Summers (STScI/AURA), D. Lennon and E. Sabbi (ESA/STScI), J. Anderson, S. E. de Mink, R. van der Marel, T. Sohn, and N. Walborn (STScI), L. Bedin (INAF, Padua), C. Evans (STFC), H. Sana (Amsterdam), N. Langer (Bonn), P. Crowther (Sheffield), A. Herrero (IAC, Tenerife), N. Bastian (USM, Munich), and E. Bressert (ESO), the Hubble Heritage Team, T. Davis, L. Frattare, Z. Levay, (Viz 3D team, STScI), J. Anderson (STScI), the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team, Eckhard Slawik (e.slawik@gmx.net); Music: Johan B. Monell (www.johanmonell.com Web and technical support: Raquel Yumi Shida Executive producer: Mariya Lyubenova]

- This year, Hubble is celebrating this new milestone with a portrait of two colorful nebulae that reveals how energetic, massive stars sculpt their homes of gas and dust. Although NGC 2014 and NGC 2020 appear to be separate in this visible-light image, they are actually part of one giant star formation complex.

- The star-forming regions seen here are dominated by the glow of stars at least 10 times more massive than our Sun. These stars have short lives of only a few million years, compared to the 10-billion-year lifetime of our Sun.

- The sparkling centerpiece of NGC 2014 is a grouping of bright, massive stars near the center of the image that has blown away its cocoon of hydrogen gas (colored red) and dust in which it was born. A torrent of ultraviolet radiation from the star cluster is illuminating the landscape around it.

- These massive stars also unleash fierce winds that are eroding the gas cloud above and to the right of them. The gas in these areas is less dense, making it easier for the stellar winds to blast through them, creating bubble-like structures reminiscent of coral, that have earned the nebula the nickname ‘Brain Coral’.

Figure 38: Pan across the Cosmic Reef: This image is one of the most photogenic examples of the many turbulent stellar nurseries the NASA/ESA Hubble Space Telescope has observed during its 30-year lifetime. The portrait features the giant nebula NGC 2014 and its neighbor NGC 2020 which together form part of a vast star-forming region in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, approximately 163,000 light-years away (video credit: NASA, ESA, and STScI)

- By contrast, the blue-colored nebula below NGC 2014 has been shaped by one mammoth star that is roughly 200,000 times more luminous than our Sun. It is an example of a rare class of stars called Wolf-Rayet stars, thought to be the descendants of the most massive stars. Wolf-Rayet stars are very luminous and have a high rate of mass loss through powerful winds.

- The star in this Hubble image is 15 times more massive than our Sun and is unleashing powerful winds, which have cleared out the area around it. It has ejected its outer layers of gas, sweeping them around into a cone-like shape, and exposing its searing hot core.

- The behemoth appears offset from the center because the telescope is viewing the cone from a slightly tilted angle. In a few million years, the star might become a supernova. The brilliant blue color of the nebula comes from oxygen gas that is heated to roughly 11,000 °C, which is much hotter than the hydrogen gas surrounding it.

Figure 39: A 3D animation of the Cosmic Reef, exploring the star-forming region featured in the Hubble's 30th anniversary image in impressive detail [video credit: NASA, ESA, G. Bacon, J. DePasquale, L. Hustak, J. Olmstead, A. Pagan, D. Player, and F. Summers (STScI). Music: "Cosmic Reef" by J. DePasquale (STScI)]

- Stars, both big and small, are born when clouds of dust and gas collapse because of gravity. As more material falls onto the forming star, it finally becomes hot and dense enough at its center to trigger the nuclear fusion reactions that make stars, including our Sun, shine.

- Massive stars make up only a few percent of the billions of stars in our Universe. Yet they play a crucial role in shaping our Universe, through stellar winds, supernova explosions, and the production of heavy elements.

- “The Hubble Space Telescope has shaped the imagination of truly a whole generation, inspiring not only scientists, but almost everybody,” said Prof. Günther Hasinger, ESA Director of Science. “It is paramount for the excellent and long-lasting cooperation between NASA and ESA.”

• 20 April 2020: On Aug. 30, 2019, when amateur astronomer Gennady Borisov gazed upward with his homemade telescope, he spotted an object moving in an unusual direction. Now called 2I/Borisov, this runaway point of light turned out to be the first confirmed comet to enter our solar system from some unknown place beyond our Sun’s influence. Astronomers everywhere rushed to take a look with some of the most powerful instruments in the world, hoping to learn as much as they could about the mysterious visitor. 40) 41)

Figure 40: This is a time-lapse sequence compressing Hubble Space Telescope observations of comet 2I/Borisov, spanning a seven-hour period. As the second known interstellar object to enter our solar system, the comet is moving along at a breakneck speed of 110,000 miles per hour (180,000 kilometers per hour). To photograph the comet Hubble has to track it, like a photographer tracking a racetrack horse. Therefore, background stars are streaked in the exposure frames. An artificial satellite also crosses the field of view. Hubble reveals a central concentration of dust around an unseen nucleus. Comet 2I/Borisov is only the second such interstellar object known to have passed through the solar system. In 2017, the first identified interstellar visitor, an object formally named 'Oumuamua', swung within 24 million miles (39 million kilometers) of the Sun before racing out of the solar system [image credit: NASA, ESA and J. DePasquale (STScI)]

- Now, thanks to observations with NASA’s Hubble Space Telescope and the National Radio Astronomy Observatory’s ALMA (Atacama Large Millimeter/submillimeter Array), astronomers have figured out that 2I/Borisov has an unusual composition. Specifically, it has a higher concentration of carbon monoxide than any comet seen at a similar distance; that is, within about 200 million miles (300 million kilometers) of the Sun.

- This suggests to scientists that the comet could have formed around a red dwarf — a smaller, fainter type of star than the Sun — though other kinds of stars are possible. Another idea is that 2I/Borisov could be a carbon monoxide-rich fragment of a small planet.

What is an interstellar comet?

- Comets are snowballs of ice, dust and frozen gas. When totally frozen (or “inactive”), they’re approximately the diameter of a small town, but when heated by the Sun their tails can extend for millions of miles. 2I/Borisov is about the length of nine football fields, or 0.61 miles (0.98 kilometers), making it relatively small. The new results on the comet’s composition are published in the journal Nature Astronomy.

- All comets form in the primordial disk of material that encircles a young star, preserving remnants of a planetary system’s ancient past. Comets from our own solar neighborhood reveal the history of materials, including water, that made Earth the planet we know today, as well as our other planetary neighbors. An interstellar comet, on the other hand, is a chemical ambassador from an entirely different star system — containing a treasure trove of clues to worlds too far to reach with modern technology.

- “With an interstellar comet passing through our own solar system, it’s like we get a sample of a planet orbiting another star showing up in our own backyard,” said John Noonan of the Lunar and Planetary Laboratory at the University of Arizona, Tucson, and a member of the Hubble research team led by Dennis Bodewits of Auburn University in Alabama.

What scientists found

- Bodewits and colleagues used Hubble to look at 2I/Borisov from Dec. 11, 2019 to Jan. 13, 2020. Separately, a team of international scientists led by Martin Cordiner and Stefanie Milam at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, studied the comet on December 15 and 16, 2019, with ALMA, an array of radio telescopes at an altitude of 5,050 meters in northern Chile. Radio telescopes are especially useful for looking at cold, low-energy gas in objects like comets.

- Results from both Hubble and ALMA estimate that 2I/Borisov’s carbon monoxide concentration is higher than that of the average solar system comet.

Where did it come from?

- A high carbon-monoxide-to-water ratio suggests that the comet has traveled from a very cold place — as cold as the area where Pluto is in relation to our Sun, called the Kuiper Belt. The group using Hubble additionally theorizes 2I/Borisov may have originated around the most common type of star in the Milky Way: a red dwarf. Red dwarfs are much smaller and dimmer than the Sun, so the planet-forming material around them would be colder than the building blocks of our solar system.

- “These stars have exactly the low temperatures and luminosities where a comet could form with the type of composition found in comet 2I/Borisov,” said Noonan.

- Scientists using ALMA say it’s possible that 2I/Borisov could be a fragment of a dwarf planet that had a lot of carbon monoxide near its surface, regardless of which type of star it came from. “If that object collided with another, then the carbon monoxide-rich fragments could be released into space,” said Cordiner.

- But 2I/Borisov may have simply formed as a comet with a high concentration of carbon monoxide, the ALMA team points out. Alternatively, it may have an unusually thick outer layer that insulates frozen gases like hydrogen cyanide and water. As the more volatile carbon monoxide evaporates or “outgasses,” it may appear more abundant than other cometary gases. 2I/Borisov’s unusual properties may also suggest a wider diversity of carbon monoxide in comets in our own solar system than previously thought.

- “Whatever the answer is, 2I/Borisov opens up a whole new can of worms for cometary science,” says Milam, one of the scientists using ALMA.

- In our own solar system, there are two places where most comets reside: The Kuiper Belt, an area that includes Pluto; and the Oort Cloud, which is much farther away. All of these comets likely formed closer to the Sun, but may have been booted outward by the erratic movements of Jupiter and Saturn billions of years ago. These giant planets, because of their immense gravity, could have even sent comets flying toward other stars, escaping the influence of the Sun’s gravity altogether.

- Given this history, scientists using Hubble theorize that a massive planet in a red dwarf system, in an environment with frozen carbon monoxide, may have punted 2I/Borisov our way.

- “If a Jupiter-sized planet migrates inward, it could kick out a lot of these comets,” Bodewits said.

- The team using ALMA agrees that a young moving planet likely sent the comet on its way. “Then, after a cold, lonely voyage, 2I/Borisov made its close encounter with our solar system and started outgassing and showing us what it’s got inside,” Cordiner says.

Figure 41: When the scientists peeked inside the halo of gas that formed around comet 2I/Borisov as it came closer to the Sun, they detected something peculiar: 2I/Borisov was releasing gas with a greater concentration of carbon monoxide than anyone had detected in any comet at a similar distance from the Sun (video credits: NASA/ALMA)

More to come

- 2I/Borisov is only the second object astronomers have detected that definitely came from a different star system. The first was 'Oumuamua, discovered in October 2017, that whizzed by too quickly for scientists to pin down its chemistry. Whether it too is a comet, an asteroid, or something else — we may never know.

- 2I/Borisov is continuing on its path through the solar system, and will eventually head out. As more advanced telescopes and other instruments turn on and gaze out in the coming years, astronomers expect to find more interstellar objects, though they will still be rare.

- “Our solar system is so tiny compared to the distances between star systems,” Cordiner says. “For an interstellar comet to come in and hit the bullseye like Borisov did is incredible.”

- ALMA is a partnership of ESO (representing its Member States), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (South Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.

• 20 April 2020: The Hubble Space Telescope offers insight into the nature of exoplanet Fomalhaut b. What astronomers thought was a planet beyond our solar system, has now seemingly vanished from sight. Astronomers now suggest that a full-grown planet never existed in the first place. The NASA/ESA Hubble Space Telescope had instead observed an expanding cloud of very fine dust particles caused by a titanic collision between two icy asteroid-sized bodies orbiting the bright star Fomalhaut, about 25 light-years from Earth. 42)

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Figure 42: Data from the NASA/ESA Hubble Space Telescope have revealed an expanding cloud of dust produced in a collision between two large bodies orbiting the bright nearby star Fomalhaut. This is the first time such a catastrophic event around another star has been imaged (image credit: ESA/NASA, M. Kornmesser)

- “The Fomalhaut system is the ultimate test lab for all of our ideas about how exoplanets and star systems evolve,” said George Rieke of the University of Arizona’s Steward Observatory. “We do have evidence of such collisions in other systems, but none of this magnitude has ever been observed. This is a blueprint for how planets destroy each other.”

- The object was previously believed to be a planet, called Fomalhaut b, and was first announced in 2008 based on data taken in 2004 and 2006. It was clearly visible in several years of Hubble observations that revealed it as a moving dot. Unlike other directly imaged exoplanets, nagging puzzles with Fomalhaut b arose early on. The object was unusually bright in visible light, but did not have any detectable infrared heat signature. Astronomers proposed that the added brightness came from a huge shell or ring of dust encircling the object that may have been collision-related. Also, early Hubble observations suggested the object might not be following an elliptical orbit, as planets usually do.

- “These collisions are exceedingly rare and so this is a big deal that we actually get to see one,” said András Gáspár of the University of Arizona. “We believe that we were at the right place at the right time to have witnessed such an unlikely event with the Hubble Space Telescope.”

- “Our study, which analyzed all available archival Hubble data on Fomalhaut b, including the most recent images taken by Hubble, revealed several characteristics that together paint a picture that the planet-sized object may never have existed in the first place,” said Gáspár. 43) 44)

- Hubble images from 2014 showed the object had vanished, to the disbelief of the astronomers. Adding to the mystery, earlier images showed the object to continuously fade over time. “Clearly, Fomalhaut b was doing things a bona fide planet should not be doing,” said Gáspár.

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Figure 43: Illustration from the Hubble Space Telescope’s observations of Fomalhaut b’s expanding dust cloud from 2004 to 2013. The cloud was produced in a collision between two large bodies orbiting the bright nearby star Fomalhaut. This is the first time such a catastrophic event around another star has been imaged [image credit: NASA, ESA, and A. Gáspár and G. Rieke (University of Arizona)]

- The resulting interpretation is that Fomalhaut b is not a planet, but a slowly expanding cloud blasted into space as a result of a collision between two large bodies. Researchers believe the collision occurred not too long prior to the first observations taken in 2004. By now the debris cloud, consisting of dust particles around 1 micron (1/50th the diameter of a human hair), is below Hubble’s detection limit. The dust cloud is estimated to have expanded by now to a size larger than the orbit of Earth around our Sun.

- Equally confounding is that the object is not on an elliptical orbit, as expected for planets, but on an escape trajectory, or hyperbolic path. “A recently created massive dust cloud, experiencing considerable radiative forces from the central star Fomalhaut, would be placed on such a trajectory” Gáspár said, “Our model is naturally able to explain all independent observable parameters of the system: its expansion rate, its fading and its trajectory.”

- Because Fomalhaut b is presently inside a vast ring of icy debris encircling the star, the colliding bodies were likely a mixture of ice and dust, like the cometary bodies that exist in the Kuiper belt on the outer fringe of our solar system. Gáspár and Rieke estimate that each of these comet-like bodies measured about 200 kilometers across. The also suggest that the Fomalhaut system may experience one of these collision events only every 200,000 years.

- Gáspár, Rieke, and other astronomers will also be observing the Fomalhaut system with the upcoming NASA/ESA/CSA James Webb Space Telescope, which is scheduled to launch in 2021.

• 17 April 2020: This image depicts a swirling spiral galaxy named NGC 2906. - The blue speckles seen scattered across this galaxy are massive young stars, which emit hot, blue-tinged radiation as they burn through their fuel at an immense rate. The swathes of orange are a mix of older stars that have swollen and cooled, and low-mass stars that were never especially hot to begin with. Owing to their lower temperatures, these stars emit a cooler, reddish, radiation. 45)

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Figure 44: This image of NGC 2906 was captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3, an instrument installed on Hubble in 2009 during the telescope’s fourth servicing mission. Hubble observed this galaxy on the hunt for fading light from recent, nearby occurrences of objects known as supernovae (image credit: ESA/Hubble & NASA, A Filippenko; CC BY 4.0)

• 10 April 2020: At first glance, the subject of this NASA/ESA Hubble Space Telescope image looks to be a simple spiral galaxy, with two pinwheeling arms emerging from a central bar of stars and material that cuts through the galactic center. In fact, there are rings within these spiral arms, too: spirals within a spiral. 46)

- This kind of morphology is known as a multiring structure. As this description suggests, this galaxy, named NGC 2273, hosts an inner ring and two outer “pseudorings” — having so many distinct rings is rare, and makes NGC 2273 unusual. Rings are created when a galaxy’s spiral arms appear to loop around to nearly close upon one another, combined with a trick of cosmic perspective. NGC 2273’s two pseudorings are formed by two swirling sets of spiral arms coming together, and the inner ring by two arcing structures nearer to the galactic center, which seem to connect in a similar way.

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Figure 45: These rings are not the only unique feature of this galaxy. NGC 2273 is also a Seyfert galaxy, a galaxy with an extremely luminous core. In fact, the center of a galaxy such as this is powered by a supermassive black hole, and can glow brightly enough to outshine an entire galaxy like the Milky Way (image credit: ESA/Hubble & NASA, J. Greene; CC BY 4.0)

• 03 April 2020: This remarkable spiral galaxy, known as NGC 4651, may look serene and peaceful as it swirls in the vast, silent emptiness of space, but don’t be fooled — it keeps a violent secret. It is believed that this galaxy consumed another smaller galaxy to become the large and beautiful spiral that we observe today. 47)

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Figure 46: Although only a telescope like the NASA/ESA Hubble Space Telescope, which captured this image, could give us a picture this clear, NGC 4651 can also be observed with an amateur telescope — so if you have a telescope at home and a star-gazing eye, look out for this glittering carnivorous spiral (image credit: ESA/Hubble & NASA, D. Leonard; CC BY 4.0)

• 31 March 2020: Astronomers have found the best evidence for the perpetrator of a cosmic homicide: a black hole of an elusive class known as "intermediate-mass," which betrayed its existence by tearing apart a wayward star that passed too close. 48)

- Weighing in at about 50,000 times the mass of our Sun, the black hole is smaller than the supermassive black holes (at millions or billions of solar masses) that lie at the cores of large galaxies, but larger than stellar-mass black holes formed by the collapse of a massive star.

- These so-called intermediate-mass black holes (IMBHs) are a long-sought "missing link" in black hole evolution. Though there have been a few other IMBH candidates, researchers consider these new observations the strongest evidence yet for mid-sized black holes in the universe.

- It took the combined power of two X-ray observatories and the keen vision of NASA's Hubble Space Telescope to nail down the cosmic beast.

Figure 47: Astronomers have found the best evidence for a black hole of an elusive class known as “intermediate-mass,” which betrayed its existence by tearing apart a wayward star that passed too close. This exciting discovery opens the door to the possibility of many more lurking undetected in the dark, waiting to be given away by a star passing too close (video credit: NASA's Goddard Space Flight Center)

- "Intermediate-mass black holes are very elusive objects, and so it is critical to carefully consider and rule out alternative explanations for each candidate. That is what Hubble has allowed us to do for our candidate," said Dacheng Lin of the University of New Hampshire, principal investigator of the study. The results are published on March 31, 2020, in The Astrophysical Journal Letters. 49)

- The story of the discovery reads like a Sherlock Holmes story, involving the meticulous step-by-step case-building necessary to catch the culprit.

- Lin and his team used Hubble to follow up on leads from NASA's Chandra X-ray Observatory and ESA's (the European Space Agency) X-ray Multi-Mirror Mission (XMM-Newton). In 2006 these satellites detected a powerful flare of X-rays, but they could not determine whether it originated from inside or outside of our galaxy. Researchers attributed it to a star being torn apart after coming too close to a gravitationally powerful compact object, like a black hole.

- Surprisingly, the X-ray source, named 3XMM J215022.4-055108, was not located in a galaxy's center, where massive black holes normally would reside. This raised hopes that an IMBH was the culprit, but first another possible source of the X-ray flare had to be ruled out: a neutron star in our own Milky Way galaxy, cooling off after being heated to a very high temperature. Neutron stars are the crushed remnants of an exploded star.

- Hubble was pointed at the X-ray source to resolve its precise location. Deep, high-resolution imaging provides strong evidence that the X-rays emanated not from an isolated source in our galaxy, but instead in a distant, dense star cluster on the outskirts of another galaxy — just the type of place astronomers expected to find an IMBH. Previous Hubble research has shown that the mass of a black hole in the center of a galaxy is proportional to that host galaxy's central bulge. In other words, the more massive the galaxy, the more massive its black hole. Therefore, the star cluster that is home to 3XMM J215022.4-055108 may be the stripped-down core of a lower-mass dwarf galaxy that has been gravitationally and tidally disrupted by its close interactions with its current larger galaxy host.

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Figure 48: This Hubble Space Telescope image identified the location of an intermediate-mass black hole, weighing 50,000 times the mass of our Sun (making it much smaller than supermassive black holes found in the centers of galaxies). The black hole, named 3XMM J215022.4-055108, is indicated by the white circle. The elusive type of black hole was first identified in a burst of telltale X-rays emitted by hot gas from a star as it was captured and destroyed by the black hole. Hubble was needed to pinpoint the black hole's location in visible light. Hubble's deep, high-resolution imaging shows that the black hole resides inside a dense cluster of stars that is far beyond our Milky Way galaxy. The star cluster is in the vicinity of the galaxy at the center of the image. Much smaller-looking background galaxies appear sprinkled around the image, including a face-on spiral just above the central foreground galaxy. This photo was taken with Hubble's Advanced Camera for Surveys [image credits: NASA, ESA and D. Lin (University of New Hampshire)]

- IMBHs have been particularly difficult to find because they are smaller and less active than supermassive black holes; they do not have readily available sources of fuel, nor as strong a gravitational pull to draw stars and other cosmic material which would produce telltale X-ray glows. Astronomers essentially have to catch an IMBH red-handed in the act of gobbling up a star. Lin and his colleagues combed through the XMM-Newton data archive, searching hundreds of thousands of observations to find one IMBH candidate.

- The X-ray glow from the shredded star allowed astronomers to estimate the black hole's mass of 50,000 solar masses. The mass of the IMBH was estimated based on both X-ray luminosity and the spectral shape. "This is much more reliable than using X-ray luminosity alone as typically done before for previous IMBH candidates," said Lin. "The reason why we can use the spectral fits to estimate the IMBH mass for our object is that its spectral evolution showed that it has been in the thermal spectral state, a state commonly seen and well understood in accreting stellar-mass black holes."

- This object isn't the first to be considered a likely candidate for an intermediate-mass black hole. In 2009 Hubble teamed up with NASA's Swift observatory and ESA's XMM-Newton to identify what is interpreted as an IMBH, called HLX-1, located towards the edge of the galaxy ESO 243-49. It too is in the center of a young, massive cluster of blue stars that may be a stripped-down dwarf galaxy core. The X-rays come from a hot accretion disk around the black hole. "The main difference is that our object is tearing a star apart, providing strong evidence that it is a massive black hole, instead of a stellar-mass black hole as people often worry about for previous candidates including HLX-1," Lin said.

- Finding this IMBH opens the door to the possibility of many more lurking undetected in the dark, waiting to be given away by a star passing too close. Lin plans to continue his meticulous detective work, using the methods his team has proved successful. Many questions remain to be answered. Does a supermassive black hole grow from an IMBH? How do IMBHs themselves form? Are dense star clusters their favored home?

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

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Figure 49: This illustration depicts a cosmic homicide in action. A wayward star is being shredded by the intense gravitational pull of a black hole that contains tens of thousands of solar masses. The stellar remains are forming an accretion disk around the black hole. Flares of X-ray light from the super-heated gas disk alerted astronomers to the black hole's location; otherwise it lurked unknown in the dark. The elusive object is classified as an intermediate mass black hole (IMBH), as it is much less massive than the monster black holes that dwell in the centers of galaxies. Therefore, IMBHs are mostly quiescent because they do not pull in as much material, and are hard to find. Hubble observations provide evidence that the IMBH dwells inside a dense star cluster. The cluster itself may be the stripped-down core of a dwarf galaxy [image credit: NASA, ESA and D. Player (STScI)]

• 27 March 2020: NGC 4618 was discovered on 9 April 1787 by the German-British astronomer, Wilhelm Herschel, who also discovered Uranus in 1781. Only a year before discovering NGC 4618, Herschel theorized that the “foggy” objects astronomers were seeing in the night sky were likely to be large star clusters located much further away then the individual stars he could easily discern. 50)

- Since Herschel proposed his theory, astronomers have come to understand that what he was seeing was a galaxy. NGC 4618, classified as a barred spiral galaxy, has the special distinction amongst other spiral galaxies of only having one arm rotating around the center of the galaxy.

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Figure 50: Located about 21 million light-years from our galaxy in the constellation Canes Venatici, NGC 4618 has a diameter of about one third that of the Milky Way. Together with its neighbor, NGC 4625, it forms an interacting galaxy pair, which means that the two galaxies are close enough to influence each other gravitationally. These interactions may result in the two (or more) galaxies merging together to form a new formation, such as a ring galaxy (image credit: ESA/Hubble & NASA, I. Karachentsev; CC BY 4.0)

• 19 March 2020: Using the unique capabilities of NASA's Hubble Space Telescope, a team of astronomers has discovered the most energetic outflows ever witnessed in the universe. They emanate from quasars and tear across interstellar space like tsunamis, wreaking havoc on the galaxies in which the quasars live. 51)

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Figure 51: This is an artist's concept of a distant galaxy with an active quasar at its center. A quasar emits exceptionally large amounts of energy generated by a supermassive black hole fueled by infalling matter. Using the unique capabilities of the Hubble Space Telescope, astronomers have discovered that blistering radiation pressure from the vicinity of the black hole pushes material away from the galaxy's center at a fraction of the speed of light. The "quasar winds" are propelling hundreds of solar masses of material each year. This affects the entire galaxy as the material snowplows into surrounding gas and dust [image credit: NASA/ESA, and J. Olmsted (STScI)]

- Quasars are extremely remote celestial objects, emitting exceptionally large amounts of energy. Quasars contain supermassive black holes fueled by infalling matter that can shine 1,000 times brighter than their host galaxies of hundreds of billions of stars.

- As the black hole devours matter, hot gas encircles it and emits intense radiation, creating the quasar. Winds, driven by blistering radiation pressure from the vicinity of the black hole, push material away from the galaxy's center. These outflows accelerate to breathtaking velocities that are a few percent of the speed of light.

- "No other phenomena carries more mechanical energy. Over the lifetime of 10 million years, these outflows produce a million times more energy than a gamma-ray burst," explained principal investigator Nahum Arav of Virginia Tech in Blacksburg, Virginia. "The winds are pushing hundreds of solar masses of material each year. The amount of mechanical energy that these outflows carry is up to several hundreds of times higher than the luminosity of the entire Milky Way galaxy."

- The quasar winds snowplow across the galaxy's disk. Material that otherwise would have formed new stars is violently swept from the galaxy, causing star birth to cease. Radiation pushes the gas and dust to far greater distances than scientists previously thought, creating a galaxy-wide event.

- As this cosmic tsunami slams into interstellar material, the temperature at the shock front spikes to billions of degrees, where material glows largely in X-rays, but also widely across the light spectrum. Anyone witnessing this event would see a brilliant celestial display. "You'll get lots of radiation first in X-rays and gamma rays, and afterwards it will percolate to visible and infrared light," said Arav. "You'd get a huge light show—like Christmas trees all over the galaxy."

- Numerical simulations of galaxy evolution suggest that such outflows can explain some important cosmological puzzles, such as why astronomers observe so few large galaxies in the universe, and why there is a relationship between the mass of the galaxy and the mass of its central black hole. This study shows that such powerful quasar outflows should be prevalent in the early universe.

- "Both theoreticians and observers have known for decades that there is some physical process that shuts off star formation in massive galaxies, but the nature of that process has been a mystery. Putting the observed outflows into our simulations solves these outstanding problems in galactic evolution," explained eminent cosmologist Jeremiah P. Ostriker, of Columbia University in New York and Princeton University in New Jersey.

- Astronomers studied 13 quasar outflows, and they were able to clock the breakneck speed of gas being accelerated by the quasar wind by looking at spectral "fingerprints" of light from the glowing gas. The Hubble ultraviolet data show that these light absorption features created from material along the path of the light were shifted in the spectrum because of the fast motion of the gas across space. This is due to the Doppler effect, where the motion of an object compresses or stretches wavelengths of light depending on whether it is approaching or receding from us. Only Hubble has the specific range of ultraviolet sensitivity that allows for astronomers to obtain the necessary observations leading to this discovery.

- Aside from measuring the most energetic quasars ever observed, the team also discovered another outflow accelerating faster than any other. It increased from nearly 43 million miles per hour to roughly 46 million miles per hour in a three-year period. The scientists believe its acceleration will continue to increase over time.

- "Hubble's ultraviolet observations allow us to follow the whole range of energy output from quasars, from cooler gas to the extremely hot, highly ionized gas in the more massive winds," added team member Gerard Kriss of the Space Telescope Science Institute in Baltimore, Maryland. "These were previously only visible with much more difficult X-ray observations. Such powerful outflows may yield new insights into the link between the growth of a central supermassive black hole and the development of its entire host galaxy."

- The team also includes graduate student Xinfeng Xu and postdoctoral researcher Timothy Miller, both of Virginia Tech, as well as Rachel Plesha of the Space Telescope Science Institute in Baltimore, Maryland. The findings were published in a series of six papers in March 2020, as a focus issue of The Astrophysical Journal Supplements.

• 19 March 2020: As reports continue about the spread of COVID-19 (coronavirus disease), this Announcement details the updates for the planned Hubble 30th Anniversary Image Unveiling events. 52)

- The health and safety of visitors and organizers of Hubble 30 celebrations events remain our top priority. The original plan was to have unveiling events taking place on or shortly after the anniversary date of 24 April. ESA/Hubble is now shifting its vision to instead hold events in the coming months that are a general celebration of the Hubble Space Telescope’s splendid 30 years.

- We understand the spread of the coronavirus may impact the feasibility of hosting public events, particularly those with large audiences. We are therefore flexible with regard to the new dates for the Hubble Space Telescope’s 30th anniversary image to be featured at various European facilities. The showcasing of the image may form part of a general Hubble celebration event any time after the 24 April public image release, and before 30 September 2020. Instead of only display events, ESA/Hubble is encouraging a broad style of events and activities that celebrate Hubble in general, and its 30 years of scientific discoveries. As events become more widespread throughout the year, ESA/Hubble will also support activities in whatever way possible, including the provision of additional materials and possible on-site support, such as qualified representatives from ESA/Hubble who can speak at various events.

- Public health should remain paramount in this situation and ESA/Hubble is confident that the presence of the Hubble 30th anniversary image at various European locations will continue to be a source of amazement to public guests. Updates will be provided at a later date regarding the new event dates and plans, and general Hubble 30 updates will be posted on this page.

• 18 March 2020: This scene of stellar creation, captured by the NASA/ESA Hubble Space Telescope, sits near the outskirts of the famous Tarantula Nebula (Figure 52). This cloud of gas and dust, as well as the many young and massive stars surrounding it, is the perfect laboratory to study the origin of massive stars. 53)

- The bright pink cloud and the young stars surrounding it in this image taken with the NASA/ESA Hubble Space Telescope have the uninspiring name LHA 120-N 150. This region of space is located on the outskirts of the Tarantula Nebula, which is the largest known stellar nursery in the local Universe. The nebula is situated over 160,000 light-years away in the Large Magellanic Cloud, a neighboring irregular dwarf galaxy that orbits the Milky Way.

- The Large Magellanic Cloud has had one or more close encounters in the past, possibly with the Small Magellanic Cloud. These interactions have caused an episode of energetic star formation in our tiny neighbor – part of which is visible as the Tarantula Nebula.

- Also known as 30 Doradus or NGC 2070, the Tarantula Nebula owes its name to the arrangement of bright patches that somewhat resemble the legs of a tarantula. It measures nearly 1000 light-years across. Its proximity, the favorable inclination of the Large Magellanic Cloud, and the absence of intervening dust make the Tarantula Nebula one of the best laboratories in which to study the formation of stars, in particular massive stars. This nebula has an exceptionally high concentration of massive stars, often referred to as super star clusters.

- Astronomers have studied LHA 120-N 150 to learn more about the environment in which massive stars form. Theoretical models of the formation of massive stars suggest that they should form within clusters of stars; but observations indicate that up to ten percent of them also formed in isolation. The giant Tarantula Nebula with its numerous substructures is the perfect laboratory in which to resolve this puzzle as in it massive stars can be found both as members of clusters and in isolation.

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Figure 52: A massive laboratory. This image shows a region of space called LHA 120-N150. It is a substructure of the gigantic Tarantula Nebula. The latter is the largest known stellar nursery in the local Universe. The nebula is situated more than 160,000 light-years away in the Large Magellanic Cloud, a neighboring dwarf irregular galaxy that orbits the Milky Way (image credit: ESA/Hubble, NASA, I. Stephens; CC BY 4.0)

- With the help of Hubble, astronomers try to find out whether the isolated stars visible in the nebula truly formed alone or just moved away from their stellar siblings. However, such a study is not an easy task; young stars, before they are fully formed – especially massive ones – look very similar to dense clumps of dust.

- LHA 120-N 150 contains several dozen of these objects. They are a mix of unclassified sources – some probably young stellar objects and others probably dust clumps. Only detailed analysis and observations will reveal their true nature and that will help to finally solve the unanswered question of the origin of massive stars.

- Hubble has observed the Tarantula Nebula and its substructures in the past – always being interested in the formation and evolution of stars.

• 10 March 2020: A simple single-cell organism that may be growing on your lawn is helping astronomers probe the largest structures in the universe. — These organisms, called slime mold, feed on dead plant material, and they have an uncanny ability to seek out food sources. Although brainless, the organism's "genius" at creating efficient networks to reach their food goal has caught the attention of scientists. Researchers have recreated the slime mold's behavior in computer algorithms to help solve large-scale engineering problems such as finding the most efficient traffic routes in large cities, solving mazes, and pinpointing crowd evacuation routes. 54)

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Figure 53: Cosmic Web and Slime Mold: Feasting Behavior of Brainless Organisms Shows Astronomers Where to Point the Hubble Telescope (image credit: NASA)

- These organisms, called slime mold, feed on dead plant material, and they have an uncanny ability to seek out food sources. Although brainless, the organism's "genius" at creating efficient networks to reach their food goal has caught the attention of scientists. Researchers have recreated the slime mold's behavior in computer algorithms to help solve large-scale engineering problems such as finding the most efficient traffic routes in large cities, solving mazes, and pinpointing crowd evacuation routes.

- A team of astronomers has now turned to slime mold to help them trace the universe's large-scale network of filaments. Built by gravity, these vast cobweb structures, called the cosmic web, tie galaxies and clusters of galaxies together along faint bridges of gas and dark matter hundreds of millions of light-years long.

- To trace the filaments, the research team designed a computer algorithm informed by slime-mold behavior. The team seeded the algorithm with the charted positions of 37,000 galaxies and ran it to generate a filamentary map. The astronomers then used archival observations from the Hubble Space Telescope to detect and study the faint gas permeating the web at the predicted locations.

- The behavior of one of nature's humblest creatures is helping astronomers probe the largest structures in the universe.

- The single-cell organism, known as slime mold (Physarum polycephalum), builds complex filamentary networks in search of food, finding near-optimal pathways to connect different locations. In shaping the universe, gravity builds a vast cobweb structure of filaments tying galaxies and clusters of galaxies together along faint bridges hundreds of millions of light-years long. There is an uncanny resemblance between the two networks: one crafted by biological evolution, and the other by the primordial force of gravity.

- The cosmic web is the large-scale backbone of the cosmos, consisting primarily of the mysterious substance known as dark matter and laced with gas, upon which galaxies are built. Dark matter cannot be seen, but it makes up the bulk of the universe's material. The existence of a web-like structure to the universe was first hinted at in the 1985 Redshift Survey conducted at the Harvard-Smithsonian Center for Astrophysics. Since those studies, the grand scale of this filamentary structure has grown in subsequent sky surveys. The filaments form the boundaries between large voids in the universe.

- But astronomers have had a difficult time finding these elusive strands, because the gas is so dim it is hard to detect. Now a team of researchers has turned to slime mold to help them build a map of the filaments in the local universe (within 500 million light-years from Earth) and find the gas within them.

- They designed a computer algorithm, inspired by slime-mold behavior, and tested it against a computer simulation of the growth of dark matter filaments in the universe. A computer algorithm is similar to a recipe that tells a computer precisely what steps to take to solve a problem.

- The researchers then applied the slime mold algorithm to data containing the locations of 37,000 galaxies mapped by the Sloan Digital Sky Survey at distances corresponding to 300 million light-years. The algorithm produced a three-dimensional map of the underlying cosmic web structure.

- They then analyzed the ultraviolet light from 350 quasars (at much farther distances of billions of light-years) catalogued in the Hubble Spectroscopic Legacy Archive, which holds the data from NASA's Hubble Space Telescope's spectrographs. These distant cosmic flashlights are the brilliant black-hole powered cores of active galaxies, whose light shines across space and through the foreground cosmic web. Imprinted on that light was the telltale absorption signature of otherwise undetected hydrogen gas that the team analyzed at specific points along the filaments. These target locations are far from the galaxies, which allowed the research team to link the gas to the universe's large-scale structure.

- "It's really fascinating that one of the simplest forms of life actually enables insight into the very largest-scale structures in the universe," said lead researcher Joseph Burchett of the University of California (UC), Santa Cruz. "By using the slime-mold simulation to find the location of the cosmic web filaments, including those far from galaxies, we could then use the Hubble Space Telescope's archival data to detect and determine the density of the cool gas on the very outskirts of those invisible filaments. Scientists have detected signatures of this gas for several decades, and we have proven the theoretical expectation that this gas comprises the cosmic web."

- The survey further validates research that denser regions of intergalactic gas is organized into filaments that the team found stretches over 10 million light-years from galaxies. (That distance is more than 100 times the diameter of our Milky Way galaxy.)

- The researchers turned to slime mold simulations when they were searching for a way to visualize the theorized connection between the cosmic web structure and the cool gas detected in previous Hubble spectroscopic studies.

- Then team member Oskar Elek, a computational media scientist at UC Santa Cruz, discovered online the work of Sage Jenson, a Berlin-based media artist. Among Jenson's works were mesmerizing artistic visualizations showing the growth of a slime mold's tentacle-like network of food-seeking structures. Jenson's art was based on outside scientific research which detailed an algorithm for simulating the growth of slime mold.

- The research team noted a striking similarity between how the slime mold builds complex filaments to capture new food, and how gravity, in shaping the universe, constructs the cosmic web strands between galaxies and galaxy clusters.

- Based on the simulation, Elek developed a three-dimensional computer model of the buildup of slime mold to estimate the location of the cosmic web's filamentary structure.

- Although using a slime-mold-inspired simulation to pinpoint the universe's largest structures may sound bizarre at first, scientists have used computer models of these humble microorganisms, as well as grown them in petri dishes in a lab, to solve such complex problems as finding the most efficient traffic routes in large cities, solving mazes, and pinpointing crowd evacuation routes. "These are hard problems to solve for a human, let alone a computer algorithm," Elek said.

- "You can almost see, especially in the map of galaxies in the local universe from the Sloan data, where the filaments should be," Burchett explained. "The slime-mold model fits that intuition impressively. The structure that you know should be there is all of a sudden found by the computer algorithm. There was no other known method that was well suited to this problem for our research."

- The researchers say that it is very difficult to design a reliable algorithm for finding the filaments in such a large survey of galaxies. "So it's quite amazing to see that the virtual slime mold gives you a very close approximation in just minutes," Elek explained. "You can literally watch it grow." Just for comparison, growing the organism in a petri dish takes days. Slime mold actually has a very special kind of intelligence for solving this one spatial task. After all, it's critical to its survival. 55)

• 09 March 2020: Hubble investigates hungry Galaxy. The astronomers are now using the NASA/ESA Hubble Space Telescope to test this interpretation. Hubble has observed such events before, so the scientists are confident that Hubble will be able to provide smoking gun evidence in the form of stellar debris that was ejected during the disruption event. 56)

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Figure 54: The subject of this image taken by the NASA/ESA Hubble Space Telescope, a spiral galaxy named NGC 1589, was once the scene of a violent bout of cosmic hunger pangs. As astronomers looked on, a poor, hapless star was seemingly torn apart and devoured by the ravenous supermassive black hole at the center of the galaxy (image credit: ESA/Hubble & NASA; CC BY 4.0)

21 February 2020: In recognition of the NASA Hubble Space Telescope's 30 years of civilization-changing astronomical discoveries, the Smithsonian National Air and Space Museum (NASM) in Washington, D.C., has awarded its 2020 Collins Trophy for Current Achievement to the Hubble operations team at the Space Telescope Science Institute (STScI) in Baltimore and NASA's Goddard Space Flight Center in Greenbelt, Maryland. 57)

- In giving the award, the museum lauded the Hubble team’s achievements in keeping the venerable telescope a highly productive and scientifically viable space observatory. Over 30 years, the team's collective efforts have made Hubble history's most scientifically viable and celebrated telescope.

- "Through the efforts of the Hubble team the observatory has continued to produce research unachievable with any other instrument. System engineers in Hubble’s control center and science operations facility have continued to find creative ways to operate the 30-year-old spacecraft to make this revolutionary science possible and ensuring its capabilities will continue for years to come," reports NASM.

- “During its 30 years in space, Hubble has brought the universe down to Earth for all of humankind to explore. Hubble excites the imagination, inspires the soul, and teaches us that there is still much to learn about our place in the cosmos,” said STScI Director Ken Sembach. “Hubble's success would not have been possible without the close linkage of science and NASA's human exploration program, so the awarding of the Collins Trophy is especially meaningful. Hubble and Apollo are both superb examples of teamwork at its finest. It is an honor for the Space Telescope Science Institute and our employees to be an integral part of the Hubble Team, and it is with deep appreciation and great joy that we thank NASM for this recognition.”

- “The incredible images and groundbreaking science achievements of Hubble are possible only because of this extraordinary operations team of engineers, managers, technical experts and support scientists working tirelessly behind the scenes," said NASA Goddard Senior Hubble Project Scientist Jennifer Wiseman. "Every snapshot and spectrum of a planet, stellar nebula or distant galaxy is achieved because of this attentive and intertwined oversight of telescope hardware, control software, science instruments and data management. This team is keeping humanity’s premiere “eye on the sky” — Hubble — in fantastic shape for profound scientific discoveries.”

- Hubble was originally planned to operate through 2005. However, five astronaut space shuttle servicing missions to Hubble, from 1993 to 2009, continued to upgrade the telescope with advanced instruments, new electronics and on-orbit repairs.

- The Hubble operations team, consisting of engineers and scientists at NASA Goddard and STScI, is the backbone behind keeping the observatory viable between these space tune-ups, and tackling day-to-day operational challenges that are common with such a complex science facility remotely controlled in space.

- “The Hubble operations team continues to rise to the challenges presented to them, developing innovative long-term measures to ensure this national asset continues to unlock secrets of our universe,” said Greg Goulet, Lockheed Martin Hubble Project Engineering Manager at NASA Goddard. “The team has used its broad range of experience to keep the spacecraft and its instruments operating at a high level for the future. Our vision is to keep Hubble operating at its peak scientific productivity for many more years.”

- The ingenuity and dedication of Hubble's staff drive its success in two critical ways: first, they overcome the ongoing impacts of the harsh space environment, and second, they ensure Hubble continues to be a unique and powerful asset for tackling our most pressing mysteries in the next decade,” said Tom Brown, STScI Hubble mission head.

- Servicing thousands of astronomers worldwide with science planning, scheduling and archiving, the team's efforts have yielded to date 1.4 million observations and provided data that astronomers have used to write more than 17,000 peer-reviewed scientific publications on a broad range of topics: from solar system investigation, to characterizing exoplanets, to probing galaxy evolution throughout 97% of the lifetime of the observable universe.

- "Hubble has changed humans’ fundamental understanding of the universe," the NASM award cites. -Hubble’s jaw-dropping iconic images are a visual shorthand for Hubble’s achievements. A true trailblazer, Hubble has made astronomy very relevant, engaging and accessible for people of all ages.

- NASM awards this trophy to recognize achievements involving the management or execution of a scientific or technological project, a distinguished career of service in air and space technology, or a significant contribution in chronicling the history of air and space technology. The award was established in 1985 as the National Air and Space Museum Trophy, but renamed in 2020 in honor of Michael Collins, the Apollo 11 astronaut who flew the command module around the Moon while Neil Armstrong and Buzz Aldrin walked on the surface.

• 20 February 2020: Surprising new data from NASA's Hubble Space Telescope suggests the smooth, settled "brim" of the Sombrero galaxy's disk may be concealing a turbulent past. Hubble's sharpness and sensitivity resolves tens of thousands of individual stars in the Sombrero's vast, extended halo, the region beyond a galaxy's central portion, typically made of older stars. These latest observations of the Sombrero are turning conventional theory on its head, showing only a tiny fraction of older, metal-poor stars in the halo, plus an unexpected abundance of metal-rich stars typically found only in a galaxy's disk, and the central bulge. Past major galaxy mergers are a possible explanation, though the stately Sombrero shows none of the messy evidence of a recent merger of massive galaxies. 58)

- "The Sombrero has always been a bit of a weird galaxy, which is what makes it so interesting," said Paul Goudfrooij of the Space Telescope Science Institute (STScI), Baltimore, Maryland. "Hubble's metallicity measurements (i.e., the abundance of heavy elements in the stars) are another indication that the Sombrero has a lot to teach us about galaxy assembly and evolution."

- ”Hubble's observations of the Sombrero's halo are turning our generally accepted understanding of galaxy makeup and metallicity on its head," added co-investigator Roger Cohen of STScI.

- Long a favorite of astronomers and amateur sky watchers alike for its bright beauty and curious structure, the Sombrero galaxy (M104) now has a new chapter in its strange story — an extended halo of metal-rich stars with barely a sign of the expected metal-poor stars that have been observed in the halos of other galaxies. Researchers, puzzling over the data from Hubble, turned to sophisticated computer models to suggest explanations for the perplexing inversion of conventional galactic theory. Those results suggest the equally surprising possibility of major mergers in the galaxy's past, though the Sombrero's majestic structure bears no evidence of recent disruption. The unusual findings and possible explanations are published in the Astrophysical Journal.

- "The absence of metal-poor stars was a big surprise," said Goudfrooij, "and the abundance of metal-rich stars only added to the mystery."

- In a galaxy's halo astronomers expect to find earlier generations of stars with less heavy elements, called metals, as compared to the crowded stellar cities in the main disk of a galaxy. Elements are created through the stellar "lifecycle" process, and the longer a galaxy has had stars going through this cycle, the more element-rich the gas and the higher-metallicity the stars that form from that gas. These younger, high-metallicity stars are typically found in the main disk of the galaxy where the stellar population is denser — or so goes the conventional wisdom.

- Complicating the facts is the presence of many old, metal-poor globular clusters of stars. These older, metal-poor stars are expected to eventually move out of their clusters and become part of the general stellar halo, but that process seems to have been inefficient in the Sombrero galaxy. The team compared their results with recent computer simulations to see what could be the origin of such unexpected metallicity measurements in the galaxy's halo.

- The results also defied expectations, indicating that the unperturbed Sombrero had undergone major accretion, or merger, events billions of years ago. Unlike our Milky Way galaxy, which is thought to have swallowed up many small satellite galaxies in so-called "minor" accretions over billions of years, a major accretion is the merger of two or more similarly massive galaxies that are rich in later-generation, higher-metallicity stars.

- The satellite galaxies only contained low-metallicity stars that were largely hydrogen and helium from the big bang. Heavier elements had to be cooked up in stellar interiors through nucleosynthesis and incorporated into later-generation stars. This process was rather ineffective in dwarf galaxies such as those around our Milky Way, and more effective in larger, more evolved galaxies.

- The results for the Sombrero are surprising because its smooth disk shows no signs of disruption. By comparison, numerous interacting galaxies, like the iconic Antennae galaxies, get their name from the distorted appearance of their spiral arms due to the tidal forces of their interaction. Mergers of similarly massive galaxies typically coalesce into large, smooth elliptical galaxies with extended halos — a process that takes billions of years. But the Sombrero has never quite fit the traditional definition of either a spiral or an elliptical galaxy. It is somewhere in between — a hybrid.

- For this particular project, the team chose the Sombrero mainly for its unique morphology. They wanted to find out how such "hybrid" galaxies might have formed and assembled over time. Follow-up studies for halo metallicity distributions will be done with several galaxies at distances similar to that of the Sombrero.

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Figure 55: On the left is an image of the Sombrero galaxy (M104) that includes a portion of the much fainter halo far outside its bright disk and bulge. Hubble photographed two regions in the halo (one of which is shown by the white box). The images on the right zoom in to show the level of detail Hubble captured. The orange box, a small subset of Hubble's view, contains myriad halo stars. The stellar population increases in density closer to the galaxy's disk (bottom blue box). Each frame contains a bright globular cluster of stars, of which there are many in the galaxy's halo. The Sombrero's halo contained more metal-rich stars than expected, but even stranger was the near-absence of old, metal-poor stars typically found in the halos of massive galaxies. Many of the globular clusters, however, contain metal-poor stars. A possible explanation for the Sombrero's perplexing features is that it is the product of the merger of massive galaxies billions of years ago, even though the smooth appearance of the galaxy's disk and halo show no signs of such a huge disruption [image credits: NASA/Digitized Sky Survey/P. Goudfrooij (STScI)/The Hubble Heritage Team (STScI/AURA)]

• 14 February 2020: The spiral galaxy NGC 2008 sits center stage, its ghostly spiral arms spreading out towards us, in this image captured by the NASA/ESA Hubble Space Telescope. 59)

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Figure 56: This galaxy is located about 425 million light-years from Earth in the constellation of Pictor (The Painter’s Easel). Discovered in 1834 by astronomer John Herschel, NGC 2008 is categorized as a type Sc galaxy in the Hubble sequence, a system used to describe and classify the various morphologies of galaxies. The “S” indicates that NGC 2008 is a spiral, while the “c” means it has a relatively small central bulge and more open spiral arms. Spiral galaxies with larger central bulges tend to have more tightly wrapped arms, and are classified as Sa galaxies, while those in between are classified as type Sb (image credit: ESA/Hubble & NASA, A. Bellini; CC BY 4.0)

- Spiral galaxies are ubiquitous across the cosmos, comprising over 70% of all observed galaxies — including our own, the Milky Way. However, their ubiquity does not detract from their beauty. These grand, spiralling collections of billions of stars are among the most wondrous sights that have been captured by telescopes such as Hubble, and are firmly embedded in astronomical iconography.

• 31 January 2020: The NGC 7541 galaxy is a barred spiral galaxy with whirling, pinwheeling, spiral arms, and a bright center that is intersected by a bar of gas and stars. This bar cuts directly through the galaxy’s central region, and is thought to invigorate the region somewhat, sparking activity and fuelling myriad processes that may otherwise have never occurred or have previously ground to a halt (star formation and active galactic nuclei being key examples). We think bars exist in up to two-thirds of all spiral galaxies, including our own home, the Milky Way. 60)

- NGC 7541 is actually observed to have a higher-than-usual star formation rate, adding weight to the theory that spiral bars act as stellar nurseries, corralling and funnelling inwards the material and fuel needed to create and nurture new baby stars. Along with its nearby companion NGC 7537, the galaxy makes up a pair of galaxies located about 110 million light-years away from us.

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Figure 57: The galaxy depicted in this Picture of the Week is a barred spiral known as NGC 7541, seen here as viewed by the NASA/ESA Hubble Space Telescope, in the constellation of Pisces (The Fishes), image credit: ESA/Hubble & NASA, A. Riess et al.; CC BY 4.0

• 08 January 2020: Using NASA's Hubble Space Telescope and a new observing technique, astronomers have found that dark matter forms much smaller clumps than previously known. This result confirms one of the fundamental predictions of the widely accepted "cold dark matter" theory. — The mysterious material makes up most of the mass in the universe, yet scientists don't understand its fundamental properties. Hubble observations have provided new clues. 61) 62)

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Figure 58: Each snapshot shows four distorted images of a background quasar (an extremely bright region in the center of some distant galaxies), surrounding the core of a massive foreground galaxy. The gravity of the foreground galaxy magnifies the quasar, an effect called gravitational lensing (image credit: NASA, ESA, A. Nierenberg, T. Treu)

- All galaxies, according to this theory, form and are embedded within clouds of dark matter. Dark matter itself consists of slow-moving, or "cold," particles that come together to form structures ranging from hundreds of thousands of times the mass of the Milky Way galaxy to clumps no more massive than the heft of a commercial airplane. (In this context, "cold" refers to the particles' speed.)

- The Hubble observation yields new insights into the nature of dark matter and how it behaves. "We made a very compelling observational test for the cold dark matter model and it passes with flying colors," said Tommaso Treu of the University of California, Los Angeles (UCLA), a member of the observing team.

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Figure 59: This graphic illustrates how a faraway quasar (an extremely bright region in the center of some distant galaxies) is altered by a massive foreground galaxy. The galaxy's powerful gravity warps and magnifies the quasar's light, producing four distorted images of the quasar [image credit: NASA, ESA and D. Player (STScI)]

- Dark matter is an invisible form of matter that makes up the bulk of the universe's mass and creates the scaffolding upon which galaxies are built. Although astronomers cannot see dark matter, they can detect its presence indirectly by measuring how its gravity affects stars and galaxies. Detecting the smallest dark matter formations by looking for embedded stars can be difficult or impossible because they contain very few stars.

- While dark matter concentrations have been detected around large- and medium-sized galaxies, much smaller clumps of dark matter have not been found until now. In the absence of observational evidence for such small-scale clumps, some researchers have developed alternative theories, including "warm dark matter." This idea suggests that dark matter particles are fast moving, zipping along too quickly to merge and form smaller concentrations. The new observations do not support this scenario, finding that dark matter is "colder" than it would have to be in the warm dark matter alternative theory.

- "Dark matter is colder than we knew at smaller scales," said Anna Nierenberg of NASA's Jet Propulsion Laboratory in Pasadena, California, leader of the Hubble survey. "Astronomers have carried out other observational tests of dark matter theories before, but ours provides the strongest evidence yet for the presence of small clumps of cold dark matter. By combining the latest theoretical predictions, statistical tools and new Hubble observations, we now have a much more robust result than was previously possible."

- Hunting for dark matter concentrations devoid of stars has proved challenging. The Hubble research team, however, used a technique in which they did not need to look for the gravitational influence of stars as tracers of dark matter. The team targeted eight powerful and distant cosmic "streetlights," called quasars (regions around active black holes that emit enormous amounts of light). The astronomers measured how the light emitted by oxygen and neon gas orbiting each of the quasars' black holes is warped by the gravity of a massive foreground galaxy, which acts as a magnifying lens.

- Using this method, the team uncovered dark matter clumps along the telescope's line of sight to the quasars, as well as in and around the intervening lensing galaxies. The dark matter concentrations detected by Hubble are 1/10,000th to 1/100,000th times the mass of the Milky Way's dark matter halo. Many of these tiny groupings most likely do not contain even small galaxies, and therefore would have been impossible to detect by the traditional method of looking for embedded stars.

- The eight quasars and galaxies were aligned so precisely that the warping effect, called gravitational lensing, produced four distorted images of each quasar. The effect is like looking at a funhouse mirror. Such quadruple images of quasars are rare because of the nearly exact alignment needed between the foreground galaxy and background quasar. However, the researchers needed the multiple images to conduct a more detailed analysis.

- The presence of the dark matter clumps alters the apparent brightness and position of each distorted quasar image. Astronomers compared these measurements with predictions of how the quasar images would look without the influence of the dark matter. The researchers used the measurements to calculate the masses of the tiny dark matter concentrations. To analyze the data, the researchers also developed elaborate computing programs and intensive reconstruction techniques.

- "Imagine that each one of these eight galaxies is a giant magnifying glass," explained team member Daniel Gilman of UCLA. "Small dark matter clumps act as small cracks on the magnifying glass, altering the brightness and position of the four quasar images compared to what you would expect to see if the glass were smooth."

- The researchers used Hubble's Wide Field Camera 3 to capture the near-infrared light from each quasar and disperse it into its component colors for study with spectroscopy. Unique emissions from the background quasars are best seen in infrared light. "Hubble's observations from space allow us to make these measurements in galaxy systems that would not be accessible with the lower resolution of ground-based telescopes - and Earth's atmosphere is opaque to the infrared light we needed to observe," explained team member Simon Birrer of UCLA.

- Treu added: "It's incredible that after nearly 30 years of operation, Hubble is enabling cutting-edge views into fundamental physics and the nature of the universe that we didn't even dream of when the telescope was launched."

- The gravitational lenses were discovered by sifting through ground-based surveys such as the Sloan Digital Sky Survey and Dark Energy Survey, which provide the most detailed three-dimensional maps of the universe ever made. The quasars are located roughly 10 billion light-years from Earth; the foreground galaxies, about 2 billion light-years.

- The number of small structures detected in the study offers more clues about dark matter's nature. "The particle properties of dark matter affect how many clumps form," Nierenberg explained. "That means you can learn about the particle physics of dark matter by counting the number of small clumps."

- However, the type of particle that makes up dark matter is still a mystery. "At present, there's no direct evidence in the lab that dark matter particles exist," Birrer said. "Particle physicists would not even talk about dark matter if the cosmologists didn't say it's there, based on observations of its effects. When we cosmologists talk about dark matter, we're asking 'how does it govern the appearance of the universe, and on what scales?'"

- Astronomers will be able to conduct follow-up studies of dark matter using future NASA space telescopes such as the James Webb Space Telescope and the Wide Field Infrared Survey Telescope (WFIRST), both infrared observatories. Webb will be capable of efficiently obtaining these measurements for all known quadruply lensed quasars. WFIRST's sharpness and large field of view will help astronomers make observations of the entire region of space affected by the immense gravitational field of massive galaxies and galaxy clusters. This will help researchers uncover many more of these rare systems.

- The team will present its results at the 235th meeting of the American Astronomical Society in Honolulu (4-8 January 2020).

- The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington.

• 06 January 2020: To kickstart the 30th anniversary year of the NASA/ESA Hubble Space Telescope, Hubble has imaged a majestic spiral galaxy. Galaxy UGC 2885 may be the largest known in the local universe. It is 2.5 times wider than our Milky Way and contains 10 times as many stars. This galaxy is 232 million light-years away, located in the northern constellation of Perseus. 63) 64)

- Despite its gargantuan size, researchers are calling it a “gentle giant” because it looks as if it has been sitting quietly over billions of years, possibly sipping hydrogen from the filamentary structure of intergalactic space. This is fuelling modest ongoing star birth at a rate half that of our Milky Way. In fact, its supermassive central black hole is also a sleeping giant; because the galaxy does not appear to be feeding on much smaller satellite galaxies, it is starved of infalling gas.

- A number of foreground stars in our Milky Way can be seen in the image, identified by their diffraction spikes. The brightest appears to sit on top of the galaxy’s disc, though UGC 2885 is really 232 million light-years farther away. The giant galaxy is located in the northern constellation Perseus.

- The galaxy has also been nicknamed “Rubin’s galaxy”, after astronomer Vera Rubin (1928–2016), by Benne Holwerda of the University of Louisville, Kentucky, who observed the galaxy with the Hubble Space Telescope.

- “My research was in large part inspired by Vera Rubin’s work in 1980 on the size of this galaxy,” said Holwerda. Rubin measured the galaxy’s rotation, providing evidence for dark matter that makes up most of the galaxy’s mass. “We consider this a commemorative image. The goal of citing Dr. Rubin in our observation was very much part of our original Hubble proposal.”

- Researchers are still seeking to understand what led to the galaxy’s monstrous size. “It’s as big as you can make a disk galaxy without hitting anything else in space,” added Holwerda.

- One clue is that the galaxy is fairly isolated in space and doesn’t have any nearby galaxies to crash into and disrupt the shape of its disc.

- Did the monster galaxy gobble up much smaller satellite galaxies over time? Or did it just slowly accrete gas to make new stars? “It seems like it’s been puttering along, slowly growing,” Holwerda said. Using Hubble’s exceptional resolution, his team is counting the number of globular star clusters in the galaxy’s halo — a vast shell of faint stars surrounding the galaxy. An excess of clusters would yield evidence that they were captured from smaller infalling galaxies over many billions of years.

- The upcoming NASA/ESA/CSA James Webb Space Telescope could be used to explore the center of this galaxy as well as the globular cluster population. The infrared capability of this telescope will give researchers a less impeded view of the underlying stellar populations that will complement Hubble’s visible-light ability to track wispy star formation throughout the galaxy.

Hubble_Auto0

Figure 60: This Hubble Space Telescope photograph showcases the majestic spiral galaxy UGC 2885, located 232 million light-years away in the northern constellation Perseus. The galaxy is 2.5 times wider than our Milky Way and contains 10 times as many stars. A number of foreground stars in our Milky Way can be seen in the image, identified by their diffraction spikes. The brightest star photobombs the galaxy's disk. The galaxy has been nicknamed "Rubin's galaxy," after astronomer Vera Rubin (1928 – 2016), who studied the galaxy's rotation rate in search of dark matter (image credit: NASA, ESA, and B. Holwerda (University of Louisville)



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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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