Minimize Hubble Space Telescope

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

• November 20, 2020: Lying in the constellation of Andromeda in the Northern hemisphere, this galaxy is classified as a spiral galaxy. Unlike the classic image of a spiral galaxy, however, the huge arms of stars and gas in UGC 12588 are very faint, undistinguished, and tightly wound around its center. The clearest view of the spiral arms comes from the bluer stars sprinkled around the edges of the galaxy that highlight the regions where new star formation is most likely taking place. 11)

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Figure 10: Observed with the NASA/ESA Hubble Space Telescope, the faint galaxy featured in this image is known as UGC 12588. Unlike many spiral galaxies, UGC 12588 displays neither a bar of stars across its centre nor the classic prominent spiral arm pattern. Instead, to a viewer, its circular, white and mostly unstructured centre makes this galaxy more reminiscent of a cinnamon bun than a mega-structure of stars and gas in space (image credit: ESA/Hubble & NASA, R. Tully; CC BY 4.0 - Acknowledgement: Gagandeep Anand)

• November 19, 2020: Some of the most stunning views of our sky occur at sunset, when sunlight pierces the clouds, creating a mixture of bright and dark rays formed by the clouds' shadows and the beams of light scattered by the atmosphere. 12)

- Astronomers studying nearby galaxy IC 5063 are tantalized by a similar effect in images taken by NASA's Hubble Space Telescope. In this case, a collection of narrow bright rays and dark shadows is seen beaming out of the blazingly bright center of the active galaxy.

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Figure 11: This Hubble Space Telescope image of the heart of nearby active galaxy IC 5063 reveals a mixture of bright rays and dark shadows coming from the blazing core, home of a supermassive black hole. Astronomers suggest that a ring of dusty material surrounding the black hole may be casting its shadow into space. According to their scenario, this interplay of light and shadow may occur when light blasted by the monster black hole strikes the dust ring, which is buried deep inside the core. Light streams through gaps in the ring, creating the brilliant cone-shaped rays. However, denser patches in the disk block some of the light, casting long, dark shadows through the galaxy. - This phenomenon is similar to sunlight piercing our Earthly clouds at sunset, creating a mixture of bright rays and dark shadows formed by beams of light scattered by the atmosphere. However, the bright rays and dark shadows appearing in IC 5063 are happening on a vastly larger scale, shooting across at least 36,000 light-years. IC 5063 resides 156 million light-years from Earth. The observations were taken on March 7 and Nov. 25, 2019 by Hubble's Wide Field Camera 3 and Advanced Camera for Surveys [image credit: NASA, ESA, STScI and W. P. Maksym (CfA)]

- A team of astronomers, led by Peter Maksym of the Center for Astrophysics | Harvard & Smithsonian (CfA), in Cambridge, Massachusetts, has traced the rays back to the galaxy's core, the location of an active supermassive black hole. A black hole is a dense, compact region of space that swallows light and matter under the crushing pull of gravity. The monster object is frenetically feeding on infalling material, producing a powerful gusher of light from superheated gas near it.

- Although the researchers have developed several plausible theories for the lightshow, the most intriguing idea suggests that an inner-tube-shaped ring, or torus, of dusty material surrounding the black hole is casting its shadow into space.

- According to Maksym's proposed scenario, the dust disk around the black hole doesn't block all of the light. Gaps in the disk allow light to beam out, creating brilliant cone-shaped rays similar to the fingers of light sometimes seen at sunset. However, the rays in IC 5063 are happening on a vastly larger scale, shooting across at least 36,000 light-years.

- Some of the light hits dense patches in the ring, casting the ring's shadow into space. These shadows appear as dark finger shapes interspersed with bright rays. These beams and shadows are visible because the black hole and its ring are tipped sideways relative to the plane of the galaxy. This alignment allows the light beams to extend far outside the galaxy.

- This interplay of light and shadow offers a unique insight into the distribution of material encircling the black hole. In some areas, the material may resemble scattered clouds. If this interpretation is correct, the observations may provide an indirect probe of the disk's mottled structure.

- "I'm most excited by the shadow of the torus idea because it's a really cool effect that I don't think we've seen before in images, although it has been hypothesized," Maksym said. "Scientifically, it's showing us something that is hard—usually impossible—to see directly. We know this phenomenon should happen, but in this case, we can see the effects throughout the galaxy. Knowing more about the geometry of the torus will have implications for anybody trying to understand the behavior of supermassive black holes and their environments. As a galaxy evolves, it is shaped by its central black hole."

- Studying the torus is important because it funnels material toward the black hole. If the "shadow" interpretation is accurate, the dark rays provide indirect evidence that the disk in IC 5063 could be very thin, which explains why light is leaking out all around the structure.

- Observations of similar black holes by NASA's Chandra X-ray Observatory detected X-rays leaking out of holes in the torus, making the structure appear like Swiss cheese. The holes may be caused by the disk being torqued by internal forces, causing it to warp, Maksym said. "It's possible that the warping creates big enough gaps for some of the light to shine through, and as the torus rotates, beams of light could sweep across the galaxy like lighthouse beams through fog," he added.

Citizen Science Serendipity

- Although astronomers have been studying the galaxy for decades, it took a non-scientist to make the surprising discovery. Judy Schmidt, an artist and amateur astronomer based in Modesto, California, uncovered the dark shadows when she reprocessed Hubble exposures of the galaxy in December 2019. Schmidt routinely culls the Hubble archive for interesting observations that she can turn into beautiful images. She shares those images on her Twitter feed with her many followers, who include astronomers such as Maksym.

- Schmidt selected the Hubble observations of IC 5063 from the archive because she is interested in galaxies that have active cores. The cone-shaped shadows were not apparent in the original exposures, so she was surprised to see them in her reprocessed image. "I had no idea they were there, and even after I'd processed it, I kept blinking my eyes wondering if I was seeing what I thought I was seeing," she said.

- She immediately posted her image to her Twitter account. "It was something I'd never seen before, and even though I had strong suspicions about them being shadow rays or 'crepuscular rays,' as Peter has dubbed them, it's easy to let one's imagination and wishful thinking run wild," she explained. "I figured if I was wrong, someone would come to ground me."

- The image prompted a lively Twitter discussion among her astronomer followers, including Maksym, who debated the rays' origin. Maksym had already been analyzing Hubble images of the jets produced by the galaxy's black hole. So he took the lead in studying the rays and writing a science paper. His study is based on near-infrared observations made by Hubble's Wide Field Camera 3 and Advanced Camera for Surveys in March and November 2019. Red and near-infrared light pierces the dusty galaxy to reveal the details that may be enshrouded in dust.

- This discovery would not have been possible without Hubble's sharp vision. The galaxy is also relatively nearby, only 156 million light-years from Earth. "Older images from telescopes on the ground showed maybe hints of this kind of structure, but the galaxy itself is such a mess that you'd never guess that this is what's going on without Hubble," Maksym explained. "Hubble has sharp pictures, is sensitive to faint things, and has a big enough field of view to image the entire galaxy."

- Maksym hopes to continue his study of the galaxy to determine whether his scenario is correct. "We will want to keep investigating, and it will be great if other scientists try to test our conclusions, too, with new observations and modeling," he said. "This is a project that is just begging for new data because it raises more questions than it answers."

- The team's results were published in The Astrophysical Journal Letters. 13)

• November 13, 2020: Gravitational lensing occurs when a large distribution of matter, such as a galaxy cluster, sits between Earth and a distant light source. As space is warped by massive objects, the light from the distant object bends as it travels to us and we see a distorted image of it. This effect was first predicted by Einstein’s general theory of relativity. 14)

- Strong gravitational lenses provide an opportunity for studying properties of distant galaxies, since Hubble can resolve details within the multiple arcs that are one of the main results of gravitational lensing. An important consequence of lensing distortion is magnification, allowing us to observe objects that would otherwise be too far away and too faint to be seen. Hubble makes use of this magnification effect to study objects beyond the sensitivity of its 2.4-meter-diameter primary mirror, showing us the most distant galaxies humanity has ever encountered.

- This lensed galaxy was found as part of the Sloan Bright Arcs Survey, which discovered some of the brightest gravitationally lensed high-redshift galaxies in the night sky.

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Figure 12: This NASA/ESA Hubble Space Telescope image features the galaxy LRG-3-817, also known as SDSS J090122.37+181432.3. The galaxy, its image distorted by the effects of gravitational lensing, appears as a long arc to the left of the central galaxy cluster (image credit: ESA/Hubble & NASA, S. Allam et al.)

• November 12, 2020: Long ago and far across the universe, an enormous burst of gamma rays unleashed more energy in a half-second than the Sun will produce over its entire 10-billion-year lifetime. In May of 2020, light from the flash finally reached Earth and was first detected by NASA's Neil Gehrels Swift Observatory. Scientists quickly enlisted other telescopes — including NASA's Hubble Space Telescope, the Very Large Array radio observatory, the W. M. Keck Observatory, and the Las Cumbres Observatory Global Telescope network — to study the explosion's aftermath and the host galaxy. It was Hubble that provided the surprise. 15)

- Based on X-ray and radio observations from the other observatories, astronomers were baffled by what they saw with Hubble: the near-infrared emission was 10 times brighter than predicted. These results challenge conventional theories of what happens in the aftermath of a short gamma-ray burst. One possibility is that the observations might point to the birth of a massive, highly magnetized neutron star called a magnetar.

- "These observations do not fit traditional explanations for short gamma-ray bursts," said study leader Wen-fai Fong of Northwestern University in Evanston, Illinois. "Given what we know about the radio and X-rays from this blast, it just doesn't match up. The near-infrared emission that we're finding with Hubble is way too bright. In terms of trying to fit the puzzle pieces of this gamma-ray burst together, one puzzle piece is not fitting correctly."

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Figure 13: This image shows the glow from a kilonova caused by the merger of two neutron stars. The kilonova, whose peak brightness reaches up to 10,000 times that of a classical nova, appears as a bright spot (indicated by the arrow) to the upper left of the host galaxy. The merger of the neutron stars is believed to have produced a magnetar, which has an extremely powerful magnetic field. The energy from that magnetar brightened the material ejected from the explosion [image credits: NASA, ESA, W. Fong (Northwestern University), and T. Laskar (University of Bath, UK)]

- Without Hubble, the gamma-ray burst would have appeared like many others, and Fong and her team would not have known about the bizarre infrared behavior. "It's amazing to me that after 10 years of studying the same type of phenomenon, we can discover unprecedented behavior like this," said Fong. "It just reveals the diversity of explosions that the universe is capable of producing, which is very exciting."

Light Fantastic

- The intense flashes of gamma rays from these bursts appear to come from jets of material that are moving extremely close to the speed of light. The jets do not contain a lot of mass — maybe a millionth of the mass of the Sun — but because they're moving so fast, they release a tremendous amount of energy across all wavelengths of light. This particular gamma-ray burst was one of the rare instances in which scientists were able to detect light across the entire electromagnetic spectrum.

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Figure 14: This illustration shows the sequence for forming a magnetar-powered kilonova, whose peak brightness reaches up to 10,000 times that of a classical nova. 1) Two orbiting neutron stars spiral closer and closer together. 2) They collide and merge, triggering an explosion that unleashes more energy in a half-second than the Sun will produce over its entire 10-billion-year lifetime. 3) The merger forms an even more massive neutron star called a magnetar, which has an extraordinarily powerful magnetic field. 4) The magnetar deposits energy into the ejected material, causing it to glow unexpectedly bright at infrared wavelengths[image credits: NASA, ESA, and D. Player (STScI)]

- "As the data were coming in, we were forming a picture of the mechanism that was producing the light we were seeing," said the study's co-investigator, Tanmoy Laskar of the University of Bath in the United Kingdom. "As we got the Hubble observations, we had to completely change our thought process, because the information that Hubble added made us realize that we had to discard our conventional thinking, and that there was a new phenomenon going on. Then we had to figure out what that meant for the physics behind these extremely energetic explosions."

- Gamma-ray bursts — the most energetic, explosive events known — live fast and die hard. They are split into two classes based on the duration of their gamma rays.

- If the gamma-ray emission is greater than two seconds, it's called a long gamma-ray burst. This event is known to result directly from the core collapse of a massive star. Scientists expect a supernova to accompany this longer type of burst.

- If the gamma-ray emission lasts less than two seconds, it's considered a short burst. This is thought to be caused by the merger of two neutron stars, extremely dense objects about the mass of the Sun compressed into the volume of a city. A neutron star is so dense that on Earth, one teaspoonful would weigh a billion tons! A merger of two neutron stars is generally thought to produce a black hole.

- Neutron star mergers are very rare but are extremely important because scientists think that they are one of the main sources of heavy elements in the universe, such as gold and uranium.

- Accompanying a short gamma-ray burst, scientists expect to see a "kilonova" whose peak brightness typically reaches 1,000 times that of a classical nova. Kilonovae are an optical and infrared glow from the radioactive decay of heavy elements and are unique to the merger of two neutron stars, or the merger of a neutron star with a small black hole.

Magnetic Monster?

- Fong and her team have discussed several possibilities to explain the unusual brightness that Hubble saw. While most short gamma-ray bursts probably result in a black hole, the two neutron stars that merged in this case may have combined to form a magnetar, a supermassive neutron star with a very powerful magnetic field.

- "You basically have these magnetic field lines that are anchored to the star that are whipping around at about a thousand times a second, and this produces a magnetized wind," explained Laskar. "These spinning field lines extract the rotational energy of the neutron star formed in the merger, and deposit that energy into the ejecta from the blast, causing the material to glow even brighter."

Figure 15: These two images taken on May 26 and July 16, 2020, show the fading light of a kilonova located in a distant galaxy. The kilonova appears as a spot to the upper left of the host galaxy. The glow is prominent in the May 26 image but fades in the July 16 image. The kilonova's peak brightness reaches up to 10,000 times that of a classical nova. A merger of two neutron stars—the source of the kilonova—is believed to have produced a magnetar, which has an extremely powerful magnetic field. The energy from that magnetar brightened the material ejected from the explosion, causing it to become unusually bright at infrared wavelengths of light [video credits: NASA, ESA, W. Fong (Northwestern University), T. Laskar (University of Bath, UK) and A. Pagan (STScI)]

- If the extra brightness came from a magnetar that deposited energy into the kilonova material, then within a few years, the team expects the ejecta from the burst to produce light that shows up at radio wavelengths. Follow-up radio observations may ultimately prove that this was a magnetar, and this may explain the origin of such objects.

- "With its amazing sensitivity at near-infrared wavelengths, Hubble really sealed the deal with this burst," explained Fong. "Amazingly, Hubble was able to take an image only three days after the burst. Through a series of later images, Hubble showed that a source faded in the aftermath of the explosion. This is as opposed to being a static source that remains unchanged. With these observations, we knew we had not only nabbed the source, but we had also discovered something extremely bright and very unusual. Hubble's angular resolution was also key in pinpointing the position of the burst and precisely measuring the light coming from the merger."

- NASA's upcoming James Webb Space Telescope is particularly well-suited for this type of observation. "Webb will completely revolutionize the study of similar events," said Edo Berger of Harvard University in Cambridge, Massachusetts, and principal investigator of the Hubble program. "With its incredible infrared sensitivity, it will not only detect such emission at even larger distances, but it will also provide detailed spectroscopic information that will resolve the nature of the infrared emission."

- The team's findings appear in an upcoming issue of The Astrophysical Journal. 16)

• November 6, 2020: The galaxy UGCA 193, seen here by the NASA/ESA Hubble Space Telescope, is a galaxy in the constellation of Sextans (The Sextant). Looking rather like a waterfall, UGCA 193 appears to host many young stars, especially in its lower portion, creating a striking blue haze and the sense that the stars are falling from “above”. 17)

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Figure 16: The blue color of UGCA 193 indicates the stars that we see are hot — some with temperatures exceeding 6 times that of our Sun. We know that cooler stars appear to our eyes more red, and hotter stars appear more blue. As the mass and surface temperature of a star, and therefore its color, are linked, heavier stars are able to “burn” at higher temperatures resulting in a blue glow from their surface (image credit: ESA/Hubble & NASA, R. Tully, CC BY 4.0)

• October 29,2020: Hubble Finds ‘Greater Pumpkin’ Galaxy Pair. In our infinite universe, if you can imagine something, you may eventually find it out there. And, that even goes for celestial objects that look like some creepy incarnation straight out of a Halloween tale. Hubble's holiday offering is a pair of colliding galaxies that resemble the cartoon Peanuts character Linus's imagining of the elusive Great Pumpkin. "Great" is an understatement in this case because the galaxy pair spans 100,000 light-years. The "pumpkin’s" glowing "eyes" are the bright, star-filled cores of each galaxy that contain supermassive black holes. An arm of newly forming stars embracing the pair gives the imaginary pumpkin a wry smirk. In about 6 billion years our Milky Way galaxy will collide with the neighboring Andromeda galaxy. When viewed from an extraterrestrial civilization far away, our collision may take on a spooky appearance too. That is, assuming they also have fertile imaginations for seeing ghostly entities among the stars. 18)

- Sorry Charlie Brown, NASA's Hubble Space Telescope is taking a peek at what might best be described as the "Greater Pumpkin," that looks like a Halloween decoration tucked away in a patch of sky cluttered with stars. What looks like two glowing eyes and a crooked carved smile is a snapshot of the early stages of a collision between two galaxies. The entire view is nearly 109,000 light-years across, approximately the diameter of our Milky Way.

- The overall pumpkin-ish color corresponds to the glow of aging red stars in two galaxies, cataloged as NGC  2292 and NGC  2293, which only have a hint of spiral structure. Yet the smile is bluish due to newborn star clusters, spread out like pearls on a necklace, along a newly forming dusty arm. The glowing eyes are concentrations of stars around a pair of supermassive black holes. The scattering of blue foreground stars makes the "pumpkin" look like it got all glittery for a Halloween party.

- What's going on in this pumpkin-like pair?

- If you mix two fried eggs together, you get something resembling scrambled eggs. The same goes for galaxy collisions throughout the universe. They lose their flattened spiral disk and the stars are scrambled into a football-shaped volume of space, forming an elliptical galaxy. But this interacting pair is a very rare example of what may turn out to result in a bigger fried egg—the construction of a giant spiral galaxy. It may depend on the specific trajectory the colliding galaxy pair is following. The encounter scenario must be rare because there's only a handful of other examples in the universe, say astronomers.

- The ghostly arm making the "smile" may be just the beginning of the process of rebuilding a spiral galaxy, say researchers. The arm embraces both galaxies. It most likely formed when interstellar gas was compressed as the two galaxies began to merge. The higher density precipitates new star formation.

- The dynamic duo hides out 120 million light-years away in the constellation Canis Major, so it is seen far behind the star-filled foreground plane of our Milky Way galaxy. Therefore, it's a difficult area to pinpoint far-flung distant background galaxies from the plethora of stars seen in the field.

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Figure 17: This is a Hubble Space Telescope snapshot of the early stages of a collision between two galaxies that resembles a Halloween carved pumpkin. The "pumpkin's" glowing “eyes” are the bright, star-filled cores of each galaxy that contain supermassive black holes. An arm of newly forming stars give the imaginary pumpkin a wry smirk. The two galaxies, cataloged as NGC  2292 and NGC  2293, are located about 120 million light-years away in the constellation Canis Major [image credit: NASA/ESA, and W. Keel (University of Alabama)]

Figure 18: Halloween is scarier with Hubble! What looks like two glowing eyes and a crooked carved smile is a snapshot of the early stages of a collision between two galaxies. This new image is just one of several spooky views Hubble has captured in the universe (video credits: NASA's Goddard Space Flight Center)

- The galaxy pair was similar to objects tagged by the citizen-science project Galaxy Zoo, where volunteers go hunting for oddball-looking galaxies. Astronomer William Keel, of the University of Alabama in Tuscaloosa, included several of these in the "Gems of the Galaxy Zoos" Hubble program, which is observing several kinds of rare galaxies during short gaps between other scheduled Hubble observations. The Hubble image brought out new details of the close encounter.

- Keel speculates that the ultimate destiny for this pair will be to merge into a giant luminous spiral galaxy like UGC 2885, Rubin's Galaxy, which is over twice the diameter of our Milky Way. Hubble has caught a snapshot of the groundbreaking early stages of a galactic makeover.

• October 23, 2020: Hubble views a galactic waterfall. 19)

- Interacting galaxies, such as these, are so named because of the influence they have on each other, which may eventually result in a merger or a unique formation. Already, these two galaxies have seemingly formed a sideways waterspout, with stars from NGC 2799 appearing to fall into NGC 2798 almost like drops of water.

- Galactic mergers can take place over several hundred million to over a billion years. While one might think the merger of two galaxies would be catastrophic for the stellar systems within, the sheer amount of space between stars means that stellar collisions are unlikely and stars typically drift past each other.

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Figure 19: In this spectacular image captured by the NASA/ESA Hubble Space Telescope, the galaxy NGC 2799 (on the left) is seemingly being pulled into the center of the galaxy NGC 2798 (on the right), [image credit: ESA/Hubble & NASA, SDSS, J. Dalcanton, CC BY 4.0; Acknowledgement: Judy Schmidt (Geckzilla)]

• October 16, 2020: When a massive new star 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 giving birth to low-mass stars. The boundary between the cool, dusty frEGG and the hot gas bubble is seen as the glowing purple/blue edges in this fascinating image. 20)

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Figure 20: This image, taken with the NASA/ESA Hubble Space Telescope, depicts a special class of star-forming nursery known as frEGGs (Free-floating Evaporating Gaseous Globules). This object is formally known as J025157.5+600606 (image credit: ESA/Hubble & NASA, R. Sahai; CC BY 4.0)

• 09 October 2020: At around 60 million light-years from Earth, the Great Barred Spiral Galaxy NGC 1365 is captured beautifully in this image by the NASA/ESA Hubble Space Telescope. Located in the constellation of Fornax (The Furnace), the blue and fiery orange swirls show us where stars have just formed and the dusty sites of future stellar nurseries. 21) 22)

- At the outer edge of the image, enormous star-forming regions within NGC 1365 can be seen. The bright, light-blue regions indicate the presence of hundreds of baby stars that formed from coalescing gas and dust within the galaxy's outer arms.

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Figure 21: This Hubble image was captured as part of a joint survey with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. The survey will help scientists understand how the diversity of galaxy environments observed in the nearby Universe, including NGC 1365 and previous ESA/Hubble Pictures of the Week such as NGC 2835 and NGC 2775, influence the formation of stars and star clusters. Expected to image over 100,000 gas clouds and star-forming regions beyond our Milky Way, the PHANGS survey is expected to uncover and clarify many of the links between cold gas clouds, star formation and the overall shape and morphology of galaxies [image credit: ESA/Hubble & NASA, J. Lee and the PHANGS-HST Team; CC BY 4.0 - Acknowledgement: Judy Schmidt (Geckzilla)]

• 02 October 2020: NGC 5643 is about 60 million light-years away from Earth and has been the host of a recent supernova event (not visible in this latest image). This supernova (2017cbv) was a specific type in which a white dwarf steals so much mass from a companion star that it becomes unstable and explodes. The explosion releases significant amounts of energy and lights up that part of the galaxy. 23)

- The observation was proposed by Adam Riess, who was awarded a Nobel Laureate in physics 2011 for his contributions to the discovery of the accelerating expansion of the Universe, alongside Saul Perlmutter and Brian Schmidt.

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Figure 22: This stunning image by the NASA/ESA Hubble Space Telescope features the spiral galaxy NGC 5643 in the constellation of Lupus (The Wolf). Looking this good isn’t easy; thirty different exposures, for a total of 9 hours observation time, together with the high resolution and clarity of Hubble, were needed to produce an image of such high level of detail and of beauty (image credit: ESA/Hubble & NASA, A. Riess et al.; CC BY 4.0; Acknowledgement: Mahdi Zamani)

• 01 October 2020: When a star unleashes as much energy in a matter of days as our Sun does in several billion years, you know it's not going to remain visible for long. 24)

- Like intergalactic paparazzi, NASA's Hubble Space Telescope captured the quick, fading celebrity status of a supernova, the self-detonation of a star. The Hubble snapshots have been assembled into a telling movie of the titanic stellar blast disappearing into oblivion in the spiral galaxy NGC 2525, located 70 million light-years away.

Figure 23: This video zooms into the barred spiral galaxy NGC 2525, located 70 million light-years away in the southern constellation Puppis. Roughly half the diameter of our Milky Way, it was discovered by British astronomer William Herschel in 1791 as a "spiral nebula." The sharpness of the image increases as we zoom into the Hubble view. As we approach an outer spiral arm a Hubble time-lapse video is inserted that shows the fading light of supernova 2018gv. Hubble didn't record the initial blast in January 2018, but for nearly one year took consecutive photos, from 2018 to 2019, that have been assembled into a time-lapse sequence. At its peak, the exploding star was as bright as 5 billion Suns [video credits: NASA, ESA, J. DePasquale (STScI), M. Kornmesser and M. Zamani (ESA/Hubble), A. Riess (STScI/JHU) and the SH0ES team, and the Digitized Sky Survey]

- Hubble began observing SN 2018gv in February 2018, after the supernova was first detected by amateur astronomer Koichi Itagaki a few weeks earlier in mid-January. Hubble astronomers were using the supernova as part of a program to precisely measure the expansion rate of the universe — a key value in understanding the physical underpinnings of the cosmos. The supernova serves as a milepost marker to measure galaxy distances, a fundamental value needed for measuring the expansion of space.

- In the time-lapse sequence, spanning nearly a year, the supernova first appears as a blazing star located on the galaxy's outer edge. It initially outshines the brightest stars in the galaxy before fading out of sight.

- "No Earthly fireworks display can compete with this supernova, captured in its fading glory by the Hubble Space Telescope," said Nobel laureate Adam Riess, of the Space Telescope Science Institute (STScI) and Johns Hopkins University in Baltimore, leader of the High-z Supernova Search Team and the Supernovae H0 for the Equation of State (SH0ES) Team to measure the universe's expansion rate.

- The type of supernova seen in this sequence originated from a burned-out star — a white dwarf located in a close binary system — that is accreting material from its companion star. When the white dwarf reaches a critical mass, its core becomes hot enough to ignite nuclear fusion, turning it into a giant atomic bomb. This thermonuclear runaway process tears the dwarf apart. The opulence is short-lived as the fireball fades away.

- Because supernovae of this type all peak at the same brightness, they are known as "standard candles," which act as cosmic tape measures. Knowing the actual brightness of the supernova and observing its brightness in the sky, astronomers can calculate the distances of their host galaxies. This allows astronomers to measure the expansion rate of the universe. Over the past 30 years Hubble has helped dramatically improve the precision of the universe's expansion rate.

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Figure 24: Astronomers using NASA's Hubble Space Telescope captured the quick, fading celebrity status of a supernova, the self-detonation of a star. The supernova, called SN 2018gv, appears in the lower left portion of the frame as a blazing star located on the outer edge of spiral galaxy NGC 2525, located 70 million light-years away [image credits: NASA, ESA, and A. Riess (STScI/JHU) and the SH0ES team; acknowledgment: M. Zamani (ESA/Hubble)]

Figure 25: The Hubble snapshots have been assembled into a telling movie of the titanic stellar blast disappearing into oblivion in the spiral galaxy NGC 2525, located 70 million light-years away. The supernova, named SN 2018gv, appears as a blazing star located on the galaxy's outer edge. It initially outshines the brightest stars in the galaxy before fading out of sight. The time-lapse video consists of observations taken from February 2018 to February 2019 [image credits: NASA, ESA, and A. Riess (STScI/JHU) and the SH0ES team; acknowledgment: M. Zamani (ESA/Hubble)]

• 25 September 2020: Resting on the tail of the Great Bear in the constellation of Ursa Major, lies NGC 5585, a spiral galaxy that is more than it appears. 25)

- The stellar disc of the galaxy extends over 35,000 light-years across. When compared with galaxies of a similar shape and size, NGC 5585 stands out by having a notably different composition: Contributing to the total mass of the galaxy, it contains a far higher proportion of dark matter.

- Hotspots of star formation can be seen along the galaxy’s faint spiral arms. These regions shine a brilliant blue, contrasting strikingly against the ever-black background of space.

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Figure 26: The many stars, and dust and gas clouds that make up NGC 5585, shown here in this Hubble image, contribute only a small fraction of the total mass of the galaxy. As in many galaxies, this discrepancy can be explained by the abundant yet seemingly invisible presence of dark matter (image credit: ESA/Hubble & NASA, R. Tully; CC BY 4.0 Acknowledgement: Gagandeep Anand)

• 18 September 2020: The twisting patterns created by the multiple spiral arms of NGC 2835 create the illusion of an eye. This is a fitting description, as this magnificent galaxy resides near the head of the southern constellation of Hydra, the water snake. This stunning barred spiral galaxy, with a width of just over half that of the Milky Way, is brilliantly featured in this image taken by the NASA/ESA Hubble Space Telescope. Although it cannot be seen in this image, a supermassive black hole with a mass millions of times that of our Sun is known to nestle in the very centre of NGC 2835. 26) 27)

- Note: PHANGS (Physics at High Angular resolution in Nearby GalaxieS) is the principal ALMA Large Program for nearby galaxies, which has obtained CO (2-1) maps for a complete sample of 74 spiral galaxies. PHANGS-HST will build the first astronomical dataset charting the connections between young stars and cold molecular gas throughout a diversity of galactic environments by imaging the 38 galaxies from PHANGS sample best suited for study of resolved stars, stellar associations, and star clusters. 28)

- Expected to image over 100,000 gas clouds and star-forming regions outside our Milky Way, this survey hopes to uncover and clarify many of the links between cold gas clouds, star formation, and the overall shape and morphology of galaxies. This initiative is a collaboration with the international Atacama Large Millimeter/submillimeter Array (ALMA) and the European Southern Observatory's Very Large Telescope's MUSE instrument, through the greater PHANGS program.

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Figure 27: This galaxy was imaged as part of PHANGS-HST, a large galaxy survey with Hubble that aims to study the connections between cold gas and young stars in a variety of galaxies in the local Universe. Within NGC 2835, this cold, dense gas produces large numbers of young stars within large star formation regions. The bright blue areas, commonly observed in the outer spiral arms of many galaxies, show where near-ultraviolet light is being emitted more strongly , indicating recent or ongoing star formation (image credit: ESA/Hubble & NASA, J. Lee, and the PHANGS-HST Team Acknowledgement: Judy Schmidt (Geckzilla); CC BY 4.0)

• 17 September 2020: A unique and exciting detail of Hubble’s new snapshot appears at mid-northern latitudes as a bright, white, stretched-out storm moving at 560 km/hr. This single plume erupted on 18 August 2020 and another has since appeared. 29) 30)

- While it’s common for storms to pop up in this region, often several at once, this particular disturbance appears to have more structure behind it than observed in previous storms. Trailing behind the plume are small, counterclockwise dark clumps also not witnessed in the past. Researchers speculate this may be the beginning of a longer-lasting northern hemisphere spot, perhaps to rival the legendary Great Red Spot that dominates the southern hemisphere.

- Hubble shows that the Great Red Spot, rolling counterclockwise in the planet’s southern hemisphere, is ploughing into the clouds ahead of it, forming a cascade of white and beige ribbons. The Great Red Spot is currently an exceptionally rich red color, with its core and outermost band appearing deeper red.

- Researchers say the Great Red Spot now measures about 15,800 km across, big enough to swallow the Earth. The super-storm is still shrinking, as noted in telescopic observations dating back to 1930, but its rate of shrinkage appears to have slowed. The reason for its dwindling size is a complete mystery.

- Researchers are noticing that another feature has changed: the Oval BA, nicknamed by astronomers as Red Spot Jr., which appears just below the Great Red Spot in this image. For the past few years, Red Spot Jr. has been fading in color to its original shade of white after appearing red in 2006. However, now the core of this storm appears to be darkening to a reddish hue. This could hint that Red Spot Jr. is on its way to reverting to a color more similar to that of its cousin.

- Hubble’s image shows that Jupiter is clearing out its higher-altitude white clouds, especially along the planet’s equator, which is enveloped in an orangish hydrocarbon smog.

- Jupiter’s icy moon Europa is visible to the left of the gas giant. Europa is already thought to harbor a liquid ocean beneath its icy crust, making this moon one of the main targets in the search for habitable worlds beyond Earth. In 2013 it was announced that the Hubble Space Telescope discovered water vapor erupting from the frigid surface of Europa, in one or more localized plumes near its south pole. ESA's JUpiter ICy moons Explorer (JUICE), a mission planned for launch in 2022, aims to explore both Jupiter and three of its largest moons: Ganymede, Callisto, and Europa.

- Hubble also captured a new multiwavelength observation in ultraviolet/visible/near-infrared light of Jupiter on 25 August 2020, which is giving researchers an entirely new view of the giant planet. Hubble’s near infrared imaging, combined with ultraviolet views, provides a unique panchromatic look that offers insights into the altitude and distribution of the planet’s haze and particles. This complements Hubble’s visible-light picture that shows the ever-changing cloud patterns.

- These new Hubble images form part of yearly maps of the entire planet taken under the OPAL (Outer Planets Atmospheres Legacy) program. The program provides yearly Hubble global views of the outer planets to look for changes in their storms, winds, and clouds.

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Figure 28: This latest image of Jupiter, taken by the NASA/ESA Hubble Space Telescope on 25 August 2020, was captured when the planet was 653 million km from Earth. Hubble’s sharp view is giving researchers an updated weather report on the monster planet’s turbulent atmosphere, including a remarkable new storm brewing, and a cousin of the Great Red Spot changing color — again. The new image also features Jupiter’s icy moon Europa (image credit: NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team; CC BY 4.0)

• 11 September 2020: Many colorful stars are packed close together in this image of the globular cluster NGC 1805, taken by the NASA/ESA Hubble Space Telescope. This tight grouping of thousands of stars is located near the edge of the Large Magellanic Cloud, a satellite galaxy of our own Milky Way. The stars orbit closely to one another, like bees swarming around a hive. In the dense centre of one of these clusters, stars are 100 to 1000 times closer together than the nearest stars are to our Sun, making planetary systems around them unlikely. 31)

- This young globular cluster can be seen from the southern hemisphere, in the Dorado constellation, which is Portuguese for dolphinfish. Usually, globular clusters contain stars which are born at the same time; however, NGC 1805 is unusual as it appears to host two different populations of stars with ages millions of years apart. Observing such clusters of stars can help astronomers understand how stars evolve, and what factors determine whether they end their lives as white dwarfs, or explode as supernovae.

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Figure 29: The striking difference in star colors is illustrated beautifully in this image, which combines two different types of light: blue stars, shining brightest in near-ultraviolet light, and red stars, illuminated in red and near-infrared. Space telescopes like Hubble can observe in the ultraviolet because they are positioned above Earth’s atmosphere, which absorbs most of this wavelength, making it inaccessible to ground-based facilities (image credit: ESA/Hubble & NASA, J. Kalirai; CC BY 4.0)

• 10 September 2020: Astronomers have discovered that there may be a missing ingredient in our cosmic recipe of how dark matter behaves. They have uncovered a discrepancy between the theoretical models of how dark matter should be distributed in galaxy clusters, and observations of dark matter's grip on clusters. 32)

Figure 30: Astronomers seem to have revealed a puzzling detail in the way dark matter behaves. They found small, dense concentrations of dark matter that bend and magnify light much more strongly than expected (video credit: NASA's Goddard Space Flight Center)

- Dark matter does not emit, absorb, or reflect light. Its presence is only known through its gravitational pull on visible matter in space. Therefore, dark matter remains as elusive as Alice in Wonderland's Cheshire Cat – where you only see its grin (in the form of gravity) but not the animal itself.

- One way astronomers can detect dark matter is by measuring how its gravity distorts space, an effect called gravitational lensing.

- Researchers found that small-scale concentrations of dark matter in clusters produce gravitational lensing effects that are 10 times stronger than expected. This evidence is based on unprecedentedly detailed observations of several massive galaxy clusters by NASA's Hubble Space Telescope and the European Southern Observatory's Very Large Telescope (VLT) in Chile.

- Galaxy clusters, the most massive structures in the universe composed of individual member galaxies, are the largest repositories of dark matter. Not only are they held together largely by dark matter's gravity, the individual cluster galaxies are themselves replete with dark matter. Dark matter in clusters is therefore distributed on both large and small scales.

- "Galaxy clusters are ideal laboratories to understand if computer simulations of the universe reliably reproduce what we can infer about dark matter and its interplay with luminous matter," said Massimo Meneghetti of the INAF (National Institute for Astrophysics)-Observatory of Astrophysics and Space Science of Bologna in Italy, the study's lead author.

- "We have done a lot of careful testing in comparing the simulations and data in this study, and our finding of the mismatch persists," Meneghetti continued. "One possible origin for this discrepancy is that we may be missing some key physics in the simulations."

- Priyamvada Natarajan of Yale University in New Haven, Connecticut, one of the senior theorists on the team, added, "There's a feature of the real universe that we are simply not capturing in our current theoretical models. This could signal a gap in our current understanding of the nature of dark matter and its properties, as these exquisite data have permitted us to probe the detailed distribution of dark matter on the smallest scales."

- The team's paper is in the September 11 issue of the journal Science. 33)

- The distribution of dark matter in clusters is mapped via the bending of light, or the gravitational lensing effect, they produce. The gravity of dark matter magnifies and warps light from distant background objects, much like a funhouse mirror, producing distortions and sometimes multiple images of the same distant galaxy. The higher the concentration of dark matter in a cluster, the more dramatic its light bending.

- Hubble's crisp images, coupled with spectra from the VLT, helped the team produce an accurate, high-fidelity dark-matter map. They identified dozens of multiply imaged, lensed, background galaxies. By measuring the lensing distortions, astronomers could trace out the amount and distribution of dark matter.

- The three key galaxy clusters used in the analysis, MACS J1206.2-0847, MACS J0416.1-2403, and Abell S1063, were part of two Hubble surveys: The Frontier Fields and the Cluster Lensing And Supernova survey with Hubble (CLASH) programs.

- To the team's surprise, the Hubble images also revealed smaller-scale arcs and distorted images nested within the larger-scale lens distortions in each cluster's core, where the most massive galaxies reside.

- The researchers believe that the embedded lenses are produced by the gravity of dense concentrations of dark matter associated with individual cluster galaxies. Dark matter's distribution in the inner regions of individual galaxies is known to enhance the cluster's overall lensing effect.

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Figure 31: This Hubble Space Telescope image shows the massive galaxy cluster MACS J1206. Embedded within the cluster are the distorted images of distant background galaxies, seen as arcs and smeared features. These distortions are caused by the amount of dark matter in the cluster, whose gravity bends and magnifies the light from faraway galaxies. This effect, called gravitational lensing, allows astronomers to study remote galaxies that would otherwise be too faint to see. Several of the cluster galaxies are sufficiently massive and dense to also distort and magnify faraway sources. The galaxies in the three pullouts represent examples of such effects. In the snapshots at upper right and bottom, two distant, blue galaxies are lensed by the foreground, redder cluster galaxies, forming rings and multiple images of the remote objects. The red blobs around the galaxy at upper left denote emission from clouds of hydrogen in a single distant source. The source, seen four times because of lensing, may be a faint galaxy. These blobs were detected by the Multi-Unit Spectroscopic Explorer (MUSE) at the European Southern Observatory's Very Large Telescope (VLT) in Chile. The blobs do not appear in the Hubble images. MACS J1206 is part of the Cluster Lensing And Supernova survey with Hubble (CLASH) and is one of three galaxy clusters the researchers studied with Hubble and the VLT. The Hubble image is a combination of visible- and infrared-light observations taken in 2011 by the Advanced Camera for Surveys and Wide Field Camera 3 (image credits: NASA, ESA, P. Natarajan (Yale University), G. Caminha (University of Groningen), M. Meneghetti (INAF-Observatory of Astrophysics and Space Science of Bologna), the CLASH-VLT/Zooming teams; acknowledgment: NASA, ESA, M. Postman (STScI), the CLASH team)

- Follow-up spectroscopic observations added to the study by measuring the velocity of the stars orbiting inside several of the cluster galaxies. "Based on our spectroscopic study, we were able to associate the galaxies with each cluster and estimate their distances," said team member Piero Rosati of the University of Ferrara in Italy.

- "The stars' speed gave us an estimate of each individual galaxy's mass, including the amount of dark matter," added team member Pietro Bergamini of the INAF-Observatory of Astrophysics and Space Science in Bologna, Italy.

- The team compared the dark-matter maps with samples of simulated galaxy clusters with similar masses, located at roughly the same distances as the observed clusters. The clusters in the computer simulations did not show the same level of dark-matter concentration on the smallest scales – the scales associated with individual cluster galaxies as seen in the universe.

- The team looks forward to continuing their stress-testing of the standard dark-matter model to pin down its intriguing nature.

- The team looks forward to continuing their stress-testing of the standard dark-matter model to pin down its intriguing nature.

- 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.

• 04 September 2020: The blue and orange stars of the faint galaxy named NGC 2188 sparkle in this image taken with the NASA/ESA Hubble Space Telescope. Although NGC 2188 appears at first glance to consist solely of a narrow band of stars, it is classified by astronomers as a barred-spiral galaxy. It appears this way from our viewpoint on Earth as the center and spiral arms of the galaxy are tilted away from us, with only the very narrow outer edge of the galaxy’s disc visible to us. Astronomers liken this occurrence to turning a dinner plate in your hands so you see only its outer edge. The true shape of the galaxy was identified by studying the distribution of the stars in the inner central bulge and outer disc and by observing the stars’ colors. 34)

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Figure 32: NGC 2188 is estimated to be just half the size of our Milky Way, at 50,000 light-years across, and it is situated in the northern hemisphere constellation of Columba (The Dove). Named in the late 1500s after Noah’s dove in biblical stories, the small constellation consists of many faint yet beautiful stars and astronomical objects (image credit: ESA/Hubble & NASA, R. Tully; CC BY 4.0)

• 28 August 2020: The original supernova explosion blasted apart a dying star about 20 times more massive than our Sun between 10,000 and 20,000 years ago. Since then, the remnant has expanded 60 light-years from its center. The shockwave marks the outer edge of the supernova remnant and continues to expand at around 350 km/s. The interaction of the ejected material and the low-density interstellar material swept up by the shockwave forms the distinctive veil-like structure seen in this image. 35)

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Figure 33: While appearing as a delicate and light veil draped across the sky, this image from the NASA/ESA Hubble Space Telescope actually depicts a small section of the Cygnus supernova blast wave, located around 2400 light-years away. The name of the supernova remnant comes from its position in the northern constellation of Cygnus (The Swan), where it covers an area 36 times larger than the full moon (image credit: SA/Hubble & NASA, W. Blair; CC BY 4.0; Acknowledgement: Leo Shatz)

• 27 August 2020: In a landmark study, scientists using NASA’s Hubble Space Telescope have mapped the immense envelope of gas, called a halo, surrounding the Andromeda galaxy, our nearest large galactic neighbor. Scientists were surprised to find that this tenuous, nearly invisible halo of diffuse plasma extends 1.3 million light-years from the galaxy—about halfway to our Milky Way—and as far as 2 million light-years in some directions. This means that Andromeda’s halo is already bumping into the halo of our own galaxy. 36)

- They also found that the halo has a layered structure, with two main nested and distinct shells of gas. This is the most comprehensive study of a halo surrounding a galaxy.

- “Understanding the huge halos of gas surrounding galaxies is immensely important,” explained co-investigator Samantha Berek of Yale University in New Haven, Connecticut. “This reservoir of gas contains fuel for future star formation within the galaxy, as well as outflows from events such as supernovae. It’s full of clues regarding the past and future evolution of the galaxy, and we’re finally able to study it in great detail in our closest galactic neighbor.”

- “We find the inner shell that extends to about a half million light-years is far more complex and dynamic,” explained study leader Nicolas Lehner of the University of Notre Dame in Indiana. “The outer shell is smoother and hotter. This difference is a likely result from the impact of supernova activity in the galaxy’s disk more directly affecting the inner halo.”

- A signature of this activity is the team’s discovery of a large amount of heavy elements in the gaseous halo of Andromeda. Heavier elements are cooked up in the interiors of stars and then ejected into space—sometimes violently as a star dies. The halo is then contaminated with this material from stellar explosions.

- The Andromeda galaxy, also known as M31, is a majestic spiral of perhaps as many as 1 trillion stars and comparable in size to our Milky Way. At a distance of 2.5 million light-years, it is so close to us that the galaxy appears as a cigar-shaped smudge of light high in the autumn sky. If its gaseous halo could be viewed with the naked eye, it would be about three times the width of the Big Dipper. This would easily be the biggest feature on the nighttime sky.

- Through a program called Project AMIGA (Absorption Map of Ionized Gas in Andromeda), the study examined the light from 43 quasars—the very distant, brilliant cores of active galaxies powered by black holes—located far beyond Andromeda. The quasars are scattered behind the halo, allowing scientists to probe multiple regions. Looking through the halo at the quasars’ light, the team observed how this light is absorbed by the Andromeda halo and how that absorption changes in different regions. The immense Andromeda halo is made of very rarified and ionized gas that doesn’t emit radiation that is easily detectable. Therefore, tracing the absorption of light coming from a background source is a better way to probe this material.

- The researchers used the unique capability of Hubble’s Cosmic Origins Spectrograph (COS) to study the ultraviolet light from the quasars. Ultraviolet light is absorbed by Earth’s atmosphere, which makes it impossible to observe with ground-based telescopes. The team used COS to detect ionized gas from carbon, silicon, and oxygen. An atom becomes ionized when radiation strips one or more electrons from it.

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Figure 34: This illustration shows the location of the 43 quasars scientists used to probe Andromeda’s gaseous halo. These quasars—the very distant, brilliant cores of active galaxies powered by black holes—are scattered far behind the halo, allowing scientists to probe multiple regions. Looking through the immense halo at the quasars’ light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the halo’s material [image credits: NASA, ESA, and E. Wheatley (STScI)]

- Andromeda’s halo has been probed before by Lehner’s team. In 2015, they discovered that the Andromeda halo is large and massive. But there was little hint of its complexity; now, it’s mapped out in more detail, leading to its size and mass being far more accurately determined.

- “Previously, there was very little information—only six quasars—within 1 million light-years of the galaxy. This new program provides much more information on this inner region of Andromeda’s halo,” explained co-investigator J. Christopher Howk, also of Notre Dame. “Probing gas within this radius is important, as it represents something of a gravitational sphere of influence for Andromeda.”

- Because we live inside the Milky Way, scientists cannot easily interpret the signature of our own galaxy’s halo. However, they believe the halos of Andromeda and the Milky Way must be very similar since these two galaxies are quite similar. The two galaxies are on a collision course, and will merge to form a giant elliptical galaxy beginning about 4 billion years from now.

- Scientists have studied gaseous halos of more distant galaxies, but those galaxies are much smaller on the sky, meaning the number of bright enough background quasars to probe their halo is usually only one per galaxy. Spatial information is therefore essentially lost. With its close proximity to Earth, the gaseous halo of Andromeda looms large on the sky, allowing for a far more extensive sampling.

- “This is truly a unique experiment because only with Andromeda do we have information on its halo along not only one or two sightlines, but over 40,” explained Lehner. “This is groundbreaking for capturing the complexity of a galaxy halo beyond our own Milky Way.”

- In fact, Andromeda is the only galaxy in the universe for which this experiment can be done now, and only with Hubble. Only with an ultraviolet-sensitive future space telescope will scientists be able to routinely undertake this type of experiment beyond the approximately 30 galaxies comprising the Local Group.

- “So Project AMIGA has also given us a glimpse of the future,” said Lehner.

- The team’s findings appear in the Aug. 27 edition of The Astrophysical Journal. 37)

- 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 35: This illustration depicts the gaseous halo of the Andromeda galaxy if it could be seen with the naked eye. At a distance of 2.5 million light-years, the majestic spiral Andromeda galaxy is so close to us that it appears as a cigar-shaped smudge of light high in the autumn sky. If its gaseous halo could be seen with the naked eye, it would be about three times the width of the Big Dipper—easily the biggest feature on the nighttime sky [image credits: NASA, ESA, J. DePasquale and E. Wheatley (STScI), and Z. Levay (background image)]

• 21 August 2020: Comet NEOWISE is the brightest comet visible from the Northern Hemisphere since 1997’s Hale-Bopp comet. It’s estimated to be travelling at over 60 km/s. The comet’s closest approach to the Sun was on 3 July and it’s now heading back to the outer reaches of the Solar System, not to pass through our neighborhood again for another 7000 years. 38)

- Hubble’s observation of NEOWISE is the first time a comet of this brightness has been photographed at such high resolution after its pass by the Sun. Earlier attempts to photograph other bright comets (such as comet ATLAS) proved unsuccessful as they disintegrated in the searing heat.

- Comets often break apart due to thermal and gravitational stresses at such close encounters, but Hubble's view suggests that NEOWISE's solid nucleus stayed intact. This heart of the comet is too small to be seen directly by Hubble. The ball of ice may be no more than 4.8 km across. But the Hubble image does captures a portion of the vast cloud of gas and dust enveloping the nucleus, which measures about 18,000 km across in this image.

- Hubble's observation also resolves a pair of jets from the nucleus shooting out in opposite directions. They emerge from the comet's core as cones of dust and gas, and then are curved into broader fan-like structures by the rotation of the nucleus. Jets are the result of ice sublimating beneath the surface with the resulting dust/gas being squeezed out at high velocity.

- The Hubble photos may also help reveal the color of the comet’s dust and how that color changes as the comet moves away from the Sun. This, in turn, may explain how solar heat affects the contents and structure of that dust and the comet’s coma. The ultimate goal here would be to determine the original properties of the dust. Researchers who used Hubble to observe the comet are currently delving further into the data to see what they’re able to find.

- Hubble has captured other well-known comet visitors throughout the past year. This includes snapping images of the breakup of comet ATLAS in April 2020 and impressive images of the interstellar comet 2I BORISOV in October 2019 and December 2019.

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Figure 36: The NASA/ESA Hubble Space Telescope has captured the closest images yet of the sky’s latest visitor to make the headlines, comet C/2020 F3 NEOWISE, after it passed by the Sun. This color image of the comet was taken on 8 August 2020. The two structures appearing on the left and right sides of the comet's center are jets of sublimating ice from beneath the surface of the nucleus, with the resulting dust and gas bring squeezed through at a high velocity. The jets emerge as cone-like structures, then are fanned out by the rotation of the comet's nucleus [image credit: NASA, ESA, Q. Zhang (California Institute of Technology), A. Pagan (STScI)]

• 21 August 2020: This galaxy was host to a supernova explosion, known as SN2015F, that was created by a white dwarf star. The white dwarf was part of a binary star system and syphoned mass from its companion, eventually becoming too greedy and taking on more than it could handle. This unbalanced the star and triggered runaway nuclear fusion that eventually led to an intensely violent supernova explosion. 39)

- SN2015F was spotted in March 2015 in the galaxy named NGC 2442, nicknamed the Meathook Galaxy owing to its extremely asymmetrical and irregular shape. The supernova shone brightly for quite some time and was easily visible from Earth through even a small telescope until later that summer.

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Figure 37: This image from the NASA/ESA Hubble Space Telescope features the spectacular galaxy NGC 2442 (image credit: ESA/Hubble & NASA, S. Smartt et al.; CC BY 4.0)

• 14 August 2020: NGC 1614 is the result of a past galactic merger which created its peculiar appearance. The cosmic collision also drove a turbulent flow of interstellar gas from the smaller of the two galaxies involved into the nucleus of the larger one, resulting in a burst of star formation which started in the core and slowly spread outwards through the galaxy. 40)

- Owing to its turbulent past and its current appearance, astronomers classify NGC 1614 as a peculiar galaxy, a starburst galaxy, and a luminous infrared galaxy. Luminous infrared galaxies are among the most luminous objects in the local Universe — and NGC 1614 is, in fact, the second most luminous galaxy within 250 million light-years.

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Figure 38: NGC 1614 is the result of a past galactic merger which created its peculiar appearance. The cosmic collision also drove a turbulent flow of interstellar gas from the smaller of the two galaxies involved into the nucleus of the larger one, resulting in a burst of star formation which started in the core and slowly spread outwards through the galaxy (image credit: ESA/Hubble & NASA, A. Adamo; CC BY 4.0)

• 13 August 2020: New observations by the NASA/ESA Hubble Space Telescope suggest that the unexpected dimming of the supergiant star Betelgeuse was most likely caused by an immense amount of hot material that was ejected into space, forming a dust cloud that blocked starlight coming from the star’s surface. 41)

- Betelgeuse is an aging, red supergiant star that has swelled in size as a result of complex, evolving changes in the nuclear fusion processes in its core. The star is so large that if it replaced the Sun at the center of our Solar System, its outer surface would extend past the orbit of Jupiter. The unprecedented phenomenon of Betelgeuse’s great dimming, eventually noticeable to even the naked eye, began in October 2019. By mid-February 2020, the brightness of this monster star had dropped by more than a factor of three.

- This sudden dimming has mystified astronomers, who sought to develop theories to account for the abrupt change. Thanks to new Hubble observations , a team of researchers now suggest that a dust cloud formed when superhot plasma was unleashed from an upwelling of a large convection cell on the star’s surface and passed through the hot atmosphere to the colder outer layers, where it cooled and formed dust. The resulting cloud blocked light from about a quarter of the star’s surface, beginning in late 2019. By April 2020, the star had returned to its normal brightness.

- Several months of Hubble’s ultraviolet-light spectroscopic observations of Betelgeuse, beginning in January 2019, produced an insightful timeline leading up to the star’s dimming. These observations provided important new clues to the mechanism behind the dimming. Hubble saw dense, heated material moving through the star’s atmosphere in September, October, and November 2019. Then, in December, several ground-based telescopes observed the star decreasing in brightness in its southern hemisphere.

- “With Hubble, we see the material as it left the star’s visible surface and moved out through the atmosphere, before the dust formed that caused the star appear to dim,” said lead researcher Andrea Dupree, associate director of The Center for Astrophysics | Harvard & Smithsonian. “We could see the effect of a dense, hot region in the southeast part of the star moving outward.”

- “This material was two to four times more luminous than the star’s normal brightness,” she continued. “And then, about a month later, the southern hemisphere of Betelgeuse dimmed conspicuously as the star grew fainter. We think it is possible that a dark cloud resulted from the outflow that Hubble detected. Only Hubble gives us this evidence of what led up to the dimming.”

- The team began using Hubble early last year to analyze the massive star. Their observations are part of a three-year Hubble study to monitor variations in the star’s outer atmosphere. The telescope’s sensitivity to ultraviolet light allowed researchers to probe the layers above the star’s surface, which are so hot that they emit mostly in the ultraviolet region of the spectrum and are not seen in visible light. These layers are heated partly by the star’s turbulent convection cells bubbling up to the surface.

- “Spatially resolving a stellar surface is only possible in favorable cases and only with the best available equipment,” said Klaus Strassmeier of the Leibniz Institute for Astrophysics Potsdam (AIP) in Germany. “In that respect, Betelgeuse and Hubble are made for each other.”

- Hubble spectra, taken in early and late 2019 and in 2020, probed the star’s outer atmosphere by measuring spectral lines of ionized magnesium. From September to November 2019, the researchers measured material passing from the star’s surface into its outer atmosphere. This hot, dense material continued to travel beyond Betelgeuse’s visible surface, reaching millions of kilometers from the star. At that distance, the material cooled down enough to form dust, the researchers said.

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Figure 39: Betelgeuse’s Dust Cloud. This artist's impression was generated using an image of Betelgeuse from late 2019 taken with the SPHERE instrument on the European Southern Observatory's Very Large Telescope (image credit: ESO, ESA/Hubble, M. Kornmesser)

- This interpretation is consistent with Hubble ultraviolet-light observations in February 2020, which showed that the behavior of the star’s outer atmosphere returned to normal, even though in visible light it was still dimming.

- Although Dupree does not know the cause of the outburst, she thinks it was aided by the star’s pulsation cycle, which continued normally though the event, as recorded by visible-light observations. Strassmeier used an automated telescope of the Leibniz Institute for Astrophysics called STELLar Activity (STELLA) to measure changes in the velocity of the gas on the star’s surface as it rose and fell during the pulsation cycle. The star was expanding in its cycle at the same time as the convective cell was upwelling. The pulsation rippling outward from Betelgeuse may have helped propel the outflowing plasma through the atmosphere.

- The red supergiant is destined to end its life in a supernova blast and some astronomers think the sudden dimming may be a pre-supernova event. The star is relatively nearby, about 725 light-years away, so the dimming event would have happened around the year 1300, as its light is just reaching Earth now.

- Dupree and her collaborators will get another chance to observe the star with Hubble in late August or early September. Right now, Betelgeuse is in the daytime sky, too close to the Sun for Hubble observations. 42)

• 07 August 2020: The barred spiral galaxy known as NGC 4907 shows its best side from 270 million light-years away to anyone who can see it from the northern hemisphere. This is a new image from the NASA/ESA Hubble Space Telescope of the face-on the galaxy, displaying its beautiful spiral arms, wound loosely around its central bright bar of stars. 43)

- NGC 4907 is also part of the Coma Cluster, a group of over 1000 galaxies, some of which can be seen around NGC 4907 in this image. This massive cluster of galaxies lies within the constellation of Coma Berenices, which is named for the locks of Queen Berenice II of Egypt: the only constellation named after a historical person.

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Figure 40: Shining brightly below the galaxy is a star that is actually within our own Milky Way galaxy. This star appears much brighter than the many millions of stars in NGC 4907 as it is 100,000 times closer, residing only 2500 light-years away (image credit: ESA/Hubble & NASA, M. Gregg; CC BY 4.0)

• 06 August 2020: Astronauts who have gazed at Earth from space have been awestruck at our blue marble planet's majesty and diversity. Mike Massimino, who helped service the Hubble Space Telescope in orbit, said, "I think of our planet as a paradise. We are very lucky to be here." 44)

- What's mind-blowing is that astronomers estimate there could be as many as 1 billion other planets like Earth in our Milky Way galaxy alone. Just imagine, one billion – not million – other "paradise planets." But it's paradise lost if nothing is living there to marvel at sunsets in azure blue skies. And, as 19th century philosopher Thomas Carlyle mused, "... what a waste of space."

- It is sobering that our home planet is the only known place in the universe where life as we know it exists and thrives. And so, we gaze outward to the stars, imprisoned by space and time, into a cosmic loneliness. That's why scientists are dedicated to building ever-larger telescopes to search for potentially habitable planets. But how will they know life is present without traveling there and watching creatures walk, fly, or slither around?

- One way is by probing a planet's atmosphere. An atmosphere with the right mix of chemical elements is necessary to nurture and sustain life. Earth's atmosphere includes oxygen, nitrogen, methane, and carbon dioxide that have helped support life for billions of years. Earth's abundance of oxygen, especially, is a clue that our atmosphere's oxygen content is being replenished by biological processes.

- Astronomers have been using a variety of ground- and space-based telescopes to analyze how the ingredients of Earth's atmosphere look from space, using our planet as a proxy for studying extrasolar planets' atmospheres. They hope to eventually compare Earth's atmospheric composition with those of other worlds to note similarities and differences. Taking advantage of a total lunar eclipse, astronomers using the Hubble telescope have detected ozone in Earth's atmosphere by looking at Earthlight reflected off the Moon. Our Moon came in handy as a giant mirror in space.

- Ozone is a key ingredient in our planet's atmosphere. It forms naturally when oxygen is exposed to strong concentrations of ultraviolet light, which triggers chemical reactions. Ozone is Earth's security blanket, protecting life from deadly ultraviolet rays.

- This is the first time a total lunar eclipse was captured at ultraviolet wavelengths and from a space telescope. This method simulates how astronomers will search for circumstantial evidence of life beyond Earth by looking for potential biosignatures on extrasolar planets.

- Using a space telescope for eclipse observations reproduces the conditions under which future telescopes would measure atmospheres of extrasolar planets that pass in front of their stars. These atmospheres may contain chemical signatures very similar to Earth, and pique our curiosity to wonder if we are not alone in the universe.

- Taking advantage of a total lunar eclipse, astronomers using NASA's Hubble Space Telescope have detected Earth's own brand of sunscreen – ozone – in our atmosphere. This method simulates how astronomers and astrobiology researchers will search for evidence of life beyond Earth by observing potential "biosignatures" on exoplanets (planets around other stars).

- Hubble did not look at Earth directly. Instead, the astronomers used the Moon as a mirror to reflect sunlight, which had passed through Earth's atmosphere, and then reflected back towards Hubble. Using a space telescope for eclipse observations reproduces the conditions under which future telescopes would measure atmospheres of transiting exoplanets. These atmospheres may contain chemicals of interest to astrobiology, the study of and search for life.

- Though numerous ground-based observations of this kind have been done previously, this is the first time a total lunar eclipse was captured at ultraviolet wavelengths and from a space telescope. Hubble detected the strong spectral fingerprint of ozone, which absorbs some of the sunlight. Ozone is important to life because it is the source of the protective shield in Earth's atmosphere.

- On Earth, photosynthesis over billions of years is responsible for our planet's high oxygen levels and thick ozone layer. That's one reason why scientists think ozone or oxygen could be a sign of life on another planet, and refer to them as biosignatures.

- "Finding ozone is significant because it is a photochemical byproduct of molecular oxygen, which is itself a byproduct of life," explained Allison Youngblood of the Laboratory for Atmospheric and Space Physics in Boulder, Colorado, lead researcher of Hubble's observations.

- Although ozone in Earth's atmosphere had been detected in previous ground-based observations during lunar eclipses, Hubble's study represents the strongest detection of the molecule to date because ozone – as measured from space with no interference from other chemicals in the Earth's atmosphere – absorbs ultraviolet light so strongly.

- Hubble recorded ozone absorbing some of the Sun's ultraviolet radiation that passed through the edge of Earth's atmosphere during a lunar eclipse that occurred on January 20 to 21, 2019. Several other ground-based telescopes also made spectroscopic observations at other wavelengths during the eclipse, searching for more of Earth's atmospheric ingredients, such as oxygen and methane.

- "One of NASA's major goals is to identify planets that could support life," Youngblood said. "But how would we know a habitable or an uninhabited planet if we saw one? What would they look like with the techniques that astronomers have at their disposal for characterizing the atmospheres of exoplanets? That's why it's important to develop models of Earth's spectrum as a template for categorizing atmospheres on extrasolar planets." 45)

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Figure 41: Hubble Observes the Total Lunar Eclipse. Taking advantage of a total lunar eclipse in January 2019, astronomers using NASA's Hubble Space Telescope have detected ozone in Earth's atmosphere. This method serves as a proxy for how they will observe Earth-like planets transiting in front of other stars in search of life. Our planet's perfect alignment with the Sun and Moon during a total lunar eclipse mimics the geometry of a transiting terrestrial planet with its star. In a new study, Hubble did not look at Earth directly. Instead, astronomers used the Moon as a mirror that reflects the sunlight transmitted through Earth's atmosphere, which was then captured by Hubble. This is the first time a total lunar eclipse was captured at ultraviolet wavelengths and from a space telescope (image credit: M. Kornmesser (ESA/Hubble), NASA and ESA)

Sniffing Out Planetary Atmospheres

- The atmospheres of some extrasolar planets can be probed if the alien world passes across the face of its parent star, an event called a transit. During a transit, starlight filters through the backlit exoplanet's atmosphere. (If viewed close up, the planet's silhouette would look like it had a thin, glowing "halo" around it caused by the illuminated atmosphere, just as Earth does when seen from space.)

- Chemicals in the atmosphere leave their telltale signature by filtering out certain colors of starlight. Astronomers using Hubble pioneered this technique for probing exoplanets. This is particularly remarkable because extrasolar planets had not yet been discovered when Hubble was launched in 1990 and the space observatory was not initially designed for such experiments.

- So far, astronomers have used Hubble to observe the atmospheres of gas giant planets and super-Earths (planets several times Earth's mass) that transit their stars. But terrestrial planets about the size of Earth are much smaller objects and their atmospheres are thinner, like the skin on an apple. Therefore, teasing out these signatures from Earth-sized exoplanets will be much harder.

- That's why researchers will need space telescopes much larger than Hubble to collect the feeble starlight passing through these small planets' atmospheres during a transit. These telescopes will need to observe planets for a longer period, many dozens of hours, to build up a strong signal.

- To prepare for these bigger telescopes, astronomers decided to conduct experiments on a much closer and only known inhabited terrestrial planet: Earth. Our planet's perfect alignment with the Sun and Moon during a total lunar eclipse mimics the geometry of a terrestrial planet transiting its star.

- But the observations were also challenging because the Moon is very bright, and its surface is not a perfect reflector because it is mottled with bright and dark areas. The Moon is also so close to Earth that Hubble had to try and keep a steady eye on one select region, despite the Moon's motion relative to the space observatory. So, Youngblood's team had to account for the Moon's drift in their analysis.

Where There's Ozone, There's Life?

- Finding ozone in the skies of a terrestrial extrasolar planet does not guarantee that life exists on the surface. "You would need other spectral signatures in addition to ozone to conclude that there was life on the planet, and these signatures cannot necessarily be seen in ultraviolet light," Youngblood said.

- On Earth, ozone is formed naturally when oxygen in the Earth's atmosphere is exposed to strong concentrations of ultraviolet light. Ozone forms a blanket around Earth, protecting it from harsh ultraviolet rays.

- "Photosynthesis might be the most productive metabolism that can evolve on any planet, because it is fueled by energy from starlight and uses cosmically abundant elements like water and carbon dioxide," said Giada Arney of NASA's Goddard Space Flight Center in Greenbelt, Maryland, a co-author of the science paper. "These necessary ingredients should be common on habitable planets."

- Seasonal variability in the ozone signature also could indicate seasonal biological production of oxygen, just as it does with the growth seasons of plants on Earth.

- But ozone can also be produced without the presence of life when nitrogen and oxygen are exposed to sunlight. To increase confidence that a given biosignature is truly produced by life, astronomers must search for combinations of biosignatures. A multiwavelength campaign is needed because each of the many biosignatures are more easily detected at wavelengths specific to those signatures.

- "Astronomers will also have to take the developmental stage of the planet into account when looking at younger stars with young planets. If you wanted to detect oxygen or ozone from a planet similar to the early Earth, when there was less oxygen in our atmosphere, the spectral features in optical and infrared light aren't strong enough," Arney explained. "We think Earth had low concentrations of ozone before the mid-Proterozoic geological period (between roughly 2.0 billion to 0.7 billion years ago) when photosynthesis contributed to the build up of oxygen and ozone in the atmosphere to the levels we see today. But because the ultraviolet-light signature of ozone features is very strong, you would have a hope of detecting small amounts of ozone. The ultraviolet may therefore be the best wavelength for detecting photosynthetic life on low-oxygen exoplanets."

- NASA has a forthcoming observatory called the James Webb Space Telescope that could make similar kinds of measurements in infrared light, with the potential to detect methane and oxygen in exoplanet atmospheres. Webb is currently scheduled to launch in 2021.

• 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. 46)

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Figure 42: 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. 47) Myriad more distant and delightfully diverse galaxies appear in the background. 48)

- 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 43: 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. 49)

- 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 44: 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 45: 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. 50)

- 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 46).

- 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 46: 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. 51)

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Figure 47: 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. 52)

- 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 48: 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. 53)

- 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 49: 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. 54)

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Figure 50: 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. 55)

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Figure 51: 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. 56)

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Figure 52: 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. 57) 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. 58)

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