Queen Berenice II’s Hair Tied Together by Dark Matter

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Coma Cluster

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Coma Cluster (uncropped view)

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Cosmoview Episode 85: Queen Berenice II’s Hair Tied Together by Dark Matter


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Zooming into the Coma Cluster


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Pan on the Coma Cluster


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Cosmoview Episodio 85: Cerro Tololo captura deslumbrante cúmulo galáctico en Chile

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The Dark Energy Camera probes the Coma Cluster, a rich cluster of galaxies named for the hair of an ancient queen and an inspiration for the theory of dark matter

The Dark Energy Camera captures an image of the dazzling Coma Cluster, named after the hair of Queen Berenice II of Egypt. Not only significant in Greek mythology, this collection of galaxies was also fundamental to the discovery of the existence of dark matter. The theory emerged in 1937 when Swiss astronomer Fritz Zwicky noticed that the Coma Cluster galaxies behaved as if they were under the influence of vast amounts of unobservable ‘dark’ matter.

This densely populated image showcases an enormous cluster not of individual stars, but of entire galaxies, known as the Coma Cluster. The Coma Cluster is named for the constellation in which it lies, Coma Berenices. It is the only one of the 88 IAU constellations [1] to be named after a historical figure. Its namesake is Queen Berenice II of Egypt, or more precisely her hair, with ‘coma’ meaning ‘hair of the head’ in Latin.

Berenice famously cut her hair off and presented it as a votive offering to the gods when her husband returned safely from war. The hair was placed in a temple, but went missing soon after. The court astronomer, Conon of Samos, claimed to identify Berenice’s lost tresses in a rather unlikely spot — the night sky — suggesting that the goddess Aphrodites had catasterized (literally turned into a constellation) the queen’s locks. This all took place around 245 BCE, meaning that Berenice’s hair has enjoyed celestial recognition for an extraordinarily long time.

The data used to build this detailed picture were collected by the Department of Energy-fabricated Dark Energy Camera (DECam), which is mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF NOIRLab. The 570-megapixel camera was built to carry out the Dark Energy Survey (DES) — an amazing 758-night run of observations between 2013 and 2019. DES was conducted with the intention to better understand the nature of dark energy — the unknown entity that is causing the expansion of our Universe to accelerate.

The Coma Cluster is closely associated with dark energy’s equally mysterious counterpart: dark matter. Nearly a century ago, in 1937, Swiss astronomer Fritz Zwicky observed several galaxies within the Coma Cluster. He calculated an approximation of the cluster’s mass based on its luminous — in other words, observable — structures. But he encountered something strange: the cluster seemed to be missing mass. In fact, the galaxies within the cluster were behaving as though the cluster contained 400 times more mass than his estimates suggested.

Zwicky reached this conclusion by observing how fast the galaxies within the cluster were moving. To explain this further, it is helpful to briefly revisit a key point about the nature of gravity. Gravity is one of the four known fundamental interactions that exist between all entities with energy or mass. The more mass that an object has, the stronger the gravitational pull it will exert. Therefore, less massive objects that are within a certain distance to a more massive object will be pulled uncontrollably towards it.

However, there is an additional factor to consider: velocity. If an object is moving fast enough, it can escape the gravitational pull of other objects. It is this principle that enabled Zwicky to infer that the Coma Cluster appeared to be ‘missing’ matter. He found that the galaxies were moving so fast that they should be escaping the cluster if it were being held together only by the observable mass. This led him to postulate that the cluster must be held together by vast amounts of unobservable ‘dark’ matter, though this suggestion seemed far-fetched to much of the astronomical community.

It took until the 1980s for the majority of astronomers to be convinced of the existence of dark matter. The consensus moved as several studies came out reporting the same curious mass inconsistency that Zwicky observed, but on the scale of single galaxies rather than entire galaxy clusters. One such study was done in 1970 by U.S. astronomers Kent Ford and Vera C. Rubin, who found evidence of invisible matter in the Andromeda Galaxy. And in 1979, astronomers Sandra Faber and John Gallagher performed a robust analysis of the mass-to-light ratio for over 50 spiral and elliptical galaxies, which led them to conclude that, “the case for invisible mass in the Universe is very strong and getting stronger.”

The existence of dark matter and dark energy is now widely accepted, and understanding their elusive nature is a main focus of modern astrophysics. A deeper understanding may be on the horizon with the upcoming 10-year Legacy Survey of Space and Time, which will be conducted by NSF–DOE Vera C. Rubin Observatory, named after the inspirational female astronomer who helped show the world that there is so much more to the Universe than meets the eye.

Source: NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab)/News

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Notes

[1] It is worth nothing that the 88 IAU constellations are just some of the imagined figures and shapes derived from the patterns of stars in the observable sky. Many more were invented by cultures throughout history.

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More information

NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory), the U.S. center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF-DOE Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

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Links:

• Explore the Coma Cluster in more detail
• Photos of the Víctor M. Blanco 4-meter Telescope
• Videos of the Víctor M. Blanco 4-meter Telescope
• Photos of DECam
• Images taken by DECam
• Check out other NOIRLab Photo Releases

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Contacts:

Josie Fenske
Jr. Public Information Officer
NSF NOIRLab
Email: josie.fenske@noirlab.edu

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Cosmic Dark Matter Web Detected in Coma Cluster

Figure 1: Dark matter in the Coma Cluster region. The distribution of dark matter calculated based on this research (dark green cloud) is overlayed on an image of the Coma Cluster and more distant background galaxies taken by the Subaru Telescope. Strands of dark matter can be seen extending millions of light years. Credit: HyeongHan et al.

The Subaru Telescope has spotted the terminal ends of dark matter filaments in the Coma Cluster stretching across millions of light years. This is the first time that strands of the cosmic web spanning the entire Universe have been directly detected. This provides new evidence to test theories about the evolution of the Universe.

In the Solar System we are used to seeing matter gathered into round objects like planets, moons, and the Sun. But dark matter, which accounts for most of the mass in the Universe, is believed to exist as a web of long thin strands. But like a spider web, these strands can be hard to see, so astronomers have typically drawn conclusions based on observations of galaxies and gas stuck in the web. This is similar to how if you see a dead leaf that appears to hang in midair, you know there is a spider web that you cannot see.

A team of researchers from Yonsei University used the Subaru Telescope to look for direct signs of dark matter filaments in the Coma Cluster, located 321 million light-years away in the direction of the constellation Coma Berenices. The Coma Cluster is one of the largest and closest galaxy clusters, making it a good place to look for faint signs of dark matter. Ironically, because it is so close, it also appears large, making it difficult to observe the entire cluster. The Subaru Telescope offers the right combination of high sensitivity, high resolution, and wide field of view, to make these observations possible. Through robust data analysis, the team identified the terminal segments of the invisible dark matter filaments attached to the Coma Cluster. This is the first time these strands have been confirmed directly, giving new evidence for the idea that dark matter webs stretch across the Universe.

These results appeared as HyeongHan et al. "Weak-lensing detection of intracluster filaments in the Coma cluster" in Nature Astronomy on January 5, 2024.

This research is based on data collected at Subaru Telescope and obtained from SMOKA, which is operated by the Astronomy Data Center, National Astronomical Observatory of Japan.

Source: Subaru Telescope

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Relevant Links

• Yonsei University January 8, 2024 Press Release

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About the Subaru Telescope

The Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan, National Institutes of Natural Sciences with the support of the MEXT Project to Promote Large Scientific Frontiers. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawai`i.

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NASA’s Webb Identifies the Earliest Strands of the Cosmic Web

ASPIRE Cosmic Filament (NIRCam Image) - (Annoted)
Credits: Image: NASA, ESA, CSA, Feige Wang (University of Arizona)
Image: Processing: Joseph DePasquale (STScI)

Caption: This deep galaxy field from Webb’s NIRCam (Near-Infrared Camera) shows an arrangement of 10 distant galaxies marked by eight white circles in a diagonal, thread-like line. (Two of the circles contain more than one galaxy.) This 3 million light-year-long filament is anchored by a very distant and luminous quasar – a galaxy with an active, supermassive black hole at its core. The quasar, called J0305-3150, appears in the middle of the cluster of three circles on the right side of the image. Its brightness outshines its host galaxy. The 10 marked galaxies existed just 830 million years after the big bang. The team believes the filament will eventually evolve into a massive cluster of galaxies.

Release Images

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Galaxies are not scattered randomly across the universe. They gather together not only into clusters, but into vast interconnected filamentary structures with gigantic barren voids in between. This “cosmic web” started out tenuous and became more distinct over time as gravity drew matter together.

Astronomers using NASA’s James Webb Space Telescope have discovered a thread-like arrangement of 10 galaxies that existed just 830 million years after the big bang. The 3 million light-year-long structure is anchored by a luminous quasar – a galaxy with an active, supermassive black hole at its core. The team believes the filament will eventually evolve into a massive cluster of galaxies, much like the well-known Coma Cluster in the nearby universe.

“I was surprised by how long and how narrow this filament is,” said team member Xiaohui Fan of the University of Arizona in Tucson. “I expected to find something, but I didn't expect such a long, distinctly thin structure.”

“This is one of the earliest filamentary structures that people have ever found associated with a distant quasar,” added Feige Wang of the University of Arizona in Tucson, the principal investigator of this program.

This discovery is from the ASPIRE project (A SPectroscopic survey of biased halos In the Reionization Era), whose main goal is to study the cosmic environments of the earliest black holes. In total, the program will observe 25 quasars that existed within the first billion years after the big bang, a time known as the Epoch of Reionization.

“The last two decades of cosmology research have given us a robust understanding of how the cosmic web forms and evolves. ASPIRE aims to understand how to incorporate the emergence of the earliest massive black holes into our current story of the formation of cosmic structure,” explained team member Joseph Hennawi of the University of California, Santa Barbara.

Growing Monsters

Another part of the study investigates the properties of eight quasars in the young universe. The team confirmed that their central black holes, which existed less than a billion years after the big bang, range in mass from 600 million to 2 billion times the mass of our Sun. Astronomers continue seeking evidence to explain how these black holes could grow so large so fast.

“To form these supermassive black holes in such a short time, two criteria must be satisfied. First, you need to start growing from a massive ‘seed’ black hole. Second, even if this seed starts with a mass equivalent to a thousand Suns, it still needs to accrete a million times more matter at the maximum possible rate for its entire lifetime,” explained Wang.

“These unprecedented observations are providing important clues about how black holes are assembled. We have learned that these black holes are situated in massive young galaxies that provide the reservoir of fuel for their growth,” said Jinyi Yang of the University of Arizona, who is leading the study of black holes with ASPIRE.

Webb also provided the best evidence yet of how early supermassive black holes potentially regulate the formation of stars in their galaxies. While supermassive black holes accrete matter, they also can power tremendous outflows of material. These winds can extend far beyond the black hole itself, on a galactic scale, and can have a significant impact on the formation of stars.

“Strong winds from black holes can suppress the formation of stars in the host galaxy. Such winds have been observed in the nearby universe but have never been directly observed in the Epoch of Reionization,” said Yang. “The scale of the wind is related to the structure of the quasar. In the Webb observations, we are seeing that such winds existed in the early universe.”

These results were published in two papers in The Astrophysical Journal Letters on June 29.

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency), and CSA (Canadian Space Agency).

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About This Release

Credits:

Media Contact:

Ann Jenkins
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science:

Feige Wang (University of Arizona), Jinyi Yang (University of Arizona), Xiaohui Fan (University of Arizona), Joseph Hennawi (UC Santa Barbara)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• Filamentary Structure Science Paper by F. Wang, et al.
• Quasar Science Paper by J. Yang, et al.

Source: NASA's James Webb Space Telescope/News

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Webb Reveals Early-Universe Prequel to Huge Galaxy Cluster

Galaxy Protocluster (NIRCam Image)
Credits: Image: NASA, ESA, CSA, Takahiro Morishita (IPAC)
Image Processing: Alyssa Pagan (STScI)

Release Images

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Every giant was once a baby, though you may never have seen them at that stage of their development. NASA’s James Webb Space Telescope has begun to shed light on formative years in the history of the universe that have thus far been beyond reach: the formation and assembly of galaxies. For the first time, a protocluster of seven galaxies has been confirmed at a distance that astronomers refer to as redshift 7.9, or a mere 650 million years after the big bang. Based on the data collected, astronomers calculated the nascent cluster’s future development, finding that it will likely grow in size and mass to resemble the Coma Cluster, a monster of the modern universe.

“This is a very special, unique site of accelerated galaxy evolution, and Webb gave us the unprecedented ability to measure the velocities of these seven galaxies and confidently confirm that they are bound together in a protocluster,” said Takahiro Morishita of IPAC-California Institute of Technology, the lead author of the study published in the Astrophysical Journal Letters.

The precise measurements captured by Webb’s Near-Infrared Spectrograph (NIRSpec) were key to confirming the galaxies’ collective distance and the high velocities at which they are moving within a halo of dark matter – more than two million miles per hour (about one thousand kilometers per second).

The spectral data allowed astronomers to model and map the future development of the gathering group, all the way to our time in the modern universe. The prediction that the protocluster will eventually resemble the Coma Cluster means that it could eventually be among the densest known galaxy collections, with thousands of members.

“We can see these distant galaxies like small drops of water in different rivers, and we can see that eventually they will all become part of one big, mighty river,” said Benedetta Vulcani of the National Institute of Astrophysics in Italy, another member of the research team.

Galaxy clusters are the greatest concentrations of mass in the known universe, which can dramatically warp the fabric of spacetime itself. This warping, called gravitational lensing, can have a magnifying effect for objects beyond the cluster, allowing astronomers to look through the cluster like a giant magnifying glass. The research team was able to utilize this effect, looking through Pandora’s Cluster to view the protocluster; even Webb’s powerful instruments need an assist from nature to see so far.

Exploring how large clusters like Pandora and Coma first came together has been difficult, due to the expansion of the universe stretching light beyond visible wavelengths into the infrared, where astronomers lacked high-resolution data before Webb. Webb’s infrared instruments were developed specifically to fill in these gaps at the beginning of the universe’s story.

The seven galaxies confirmed by Webb were first established as candidates for observation using data from the Hubble Space Telescope’s Frontier Fields program. The program dedicated Hubble time to observations using gravitational lensing, to observe very distant galaxies in detail. However, because Hubble cannot detect light beyond near-infrared, there is only so much detail it can see. Webb picked up the investigation, focusing on the galaxies scouted by Hubble and gathering detailed spectroscopic data in addition to imagery.

The research team anticipates that future collaboration between Webb and NASA’s Nancy Grace Roman Space Telescope, a high-resolution, wide-field survey mission, will yield even more results on early galaxy clusters. With 200 times Hubble's infrared field of view in a single shot, Roman will be able to identify more protocluster galaxy candidates, which Webb can follow up to confirm with its spectroscopic instruments. The Roman mission is currently targeted for launch by May 2027.

“It is amazing the science we can now dream of doing, now that we have Webb,” said Tommaso Treu of the University of California, Los Angeles, a member of the protocluster research team. “With this small protocluster of seven galaxies, at this great distance, we had a one hundred percent spectroscopic confirmation rate, demonstrating the future potential for mapping dark matter and filling in the timeline of the universe’s early development.”

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

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About This Release:

Credits:

Media Contact:

Leah Ramsay
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Takahiro Morishita (IPAC)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• Science paper by T. Morishita, et al.

Source: NASA's James Webb Space Telescope/News

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Tails Tell the Tale of Galaxy Evolution

Figure: Conceptual image of the evolutionary path from a normal dwarf galaxy to an UDG/dE in a cluster. (a) An unperturbed galaxy falls near, but not directly through, the cluster. (b) Collision with intercluster gas triggers star formation and gas stripping, creating a “jellyfish” galaxy. (c) Star formation and stripping remove all of the gas, quenching further star formation. (d) The galaxy evolves into an UDG or dwarf elliptical (dE). (Credit: Kirill Grishin, Legacy Surveys / D. Lang (Perimeter Institute), NAOJ, CFHT, ESO )

An international team of astronomers has found tails of gas and/or stars trailing behind a sample of young galaxies without current star formation. Based on this result, the team concludes that about half of the ultra-diffuse galaxies in the Coma cluster are likely to have evolved through collisions with external gas. Ultra-diffuse galaxies together with similar dwarf elliptical galaxies account for about 80% of the members of galaxy clusters, so understanding their evolution is an important part of modeling the evolution of the Universe.

Extended galaxies sparely populated by stars and exhibiting little current star formation are commonly found in galaxy clusters. It is thought that these ultra-diffuse galaxies (UDG) started as more normal dwarf galaxies, but some event removed most of the gas from the galaxies, preventing them from forming new stars, and causing them to puff up in size. But precisely because these ultra-diffuse galaxies are faint and diffuse, they are difficult to study, so their evolution remains poorly understood.

To work around this problem, an international team of astronomers from Russia, the USA, Japan, France, and the UAE, used archive data from the 8.2 m Subaru Telescope and new observations with the 6.5 m MMT to study galaxies which are currently bright, but expected to evolve into UDGs. The sample includes 9 galaxies in the Coma cluster (320 million light-years away in the direction of the constellation Coma Berenices) and 2 galaxies in the Abell 2147 cluster (510 million light-years away in the direction of the constellation Hercules). The team found that every galaxy in the sample exhibits a tail of gas and/or stars, indicating that they have recently collided with outside gas.

The space between galaxies in a cluster is not a perfect vacuum; there is very hot, thin intracluster gas. When a small galaxy passes through it, the gas inside the galaxy collides with this intracluster gas. This triggers a burst of rapid star formation, and the pressure from the intracluster gas pushes the original gas out of the galaxy. During this phase, the galaxy exhibits a bright tail or tails of gas streaming behind it, earning it the nickname “jellyfish galaxy.” The loss of gas prevents further star formation and changes the dynamics of the galaxy, causing it to puff up in size. In this way, collision with intracluster gas provides an all-in-one explanation for the evolution of UDGs. From the number of galaxies studied in this sample, the team estimates that approximately half of the UDGs in the Coma cluster have experienced this kind of gas stripping.

These results appeared as Grishin et al. "Transforming gas-rich low-mass disky galaxies into ultra-diffuse galaxies by ram pressure" in Nature Astronomy on November 1, 2021.

About the Subaru Telescope

The Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan, National Institutes of Natural Sciences with the support of the MEXT Project to Promote Large Scientific Frontiers. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawai`i.

Relevant Links

• Smithsonian Center for Astrophysics November 5, 2021 Press Release
• Lomonosov Moscow State University November 1, 2021 Press Release (Russian)
• Russian Science Foundation November 2, 2021 Press Release (Russian)

Source: Subaru Telescope/Science Results

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Jellyfish Galaxies Swimming Through Clusters

Example of a jellyfish galaxy that's undergoing tidal stripping as it moves through a galaxy cluster.
Credit: ALMA / ESO / NAOJ / NRAO / P. Jachym et al.

Galaxy clusters are the largest gravitationally bound structures in the universe, exceeded in size by only the vast cosmic web in which they are embedded. Clusters contain anything from hundreds to thousands of galaxies, which they accrete due to gravity, and they can reach several megaparsecs in size. However, galaxy clusters are not gentle giants. These huge objects contain extremely hot X-ray-emitting plasma, and they can produce gravitational tidal forces strong enough to tear galaxies apart.

Because of these cluster properties, galaxies in clusters and galaxies elsewhere in the universe (called field galaxies) can differ dramatically. Galaxies that have entered a cluster environment are more often elliptical, have low star formation rates, and contain very little gas (from which new stars are formed). This so-called morphology–density relation has been well-established for decades — and although a whole host of theories exist, the specific causes of it are still unclear.

Enter Cramer et al., the authors of today’s paper.

This work presents observations of ram-pressure stripping, a mechanism that can explain the evolution of galaxies from gas-rich to gas-poor when entering a cluster. A galaxy moving through a medium (in this case, the hot intracluster plasma) can have loosely bound gas removed by drag forces from that medium. Imagine what it would look like if you poured a bag of flour over your head, and then stuck your head out of the window of a fast-moving car (not that I’d recommend this).

Along came a Jellyfish

The authors’ evidence for ram-pressure stripping comes in the form of a jellyfish galaxy. In this case, they examine D100, a barred spiral galaxy close to the centre of the Coma cluster. Jellyfish galaxies represent an extreme example of ram-pressure stripping, where the stripped gas streams out in a long tail behind the galaxy, giving them their distinctive look. Think back to the flour-head-car-window example — you would probably expect to see something similar.

Figure 1: Left: Composite image of D100 galaxy, showing the stripped gas trailing the galaxy disc, which is moving from left to right in this image. Right: A jellyfish, for comparison. [Left: Cramer et al. 2019; right: Alexander Semenov]

Using new Hubble Space Telescope (HST) observations, this work examines both the galaxy and the long tail trailing behind, which contains far fewer stars than the main galactic disc, and so is much fainter. The photo of D100 in Figure 1 is a composite image, combining the HST observations of starlight with observations of the Hα emission line from the Subaru telescope that show the presence of excited hydrogen gas. This Hα emission is shown in bright red, and demonstrates the dramatic effect that the Coma cluster is having on this galaxy.

Hα emission from galaxies is often an indicator of ongoing star formation (although it can have other sources). However, it is the combination of Hα measurements and the powerful HST observations that make this work possible. Thanks to the exceptional resolution of Hubble, and the authors’ multiple observation bands — F814W (red/near-IR wavelengths), F475W (blue) and F275W (near-UV) — Cramer and collaborators are able to study not only how much star formation is taking place, but also where in the tail this is happening.

 A Tail of Three Bands

The authors’ colour analysis shows that star formation stopped long ago in the galaxy outskirts, but has stopped more recently closer to the centre, and it is ongoing in the core. This indicates that the star-forming gas was removed from the galaxy outskirts first, causing outside-in quenching.

Figure 2: HST image of D100. Arrow is pointing to a star-forming clump, embedded in a dark region of dust that is also being stripped. [Adapted from Cramer et al. 2019]

A zoom-in on the HST image (Figure 2) also reveals a small, bright patch, located in a cloud of dust. The colour of this patch, which is bright in the blue and UV bands and fainter in red, indicates that it is a clump of ongoing star formation. In fact, the HST observations find 37 bright patches (shown in Figure 3), and analysis of their colours shows 10 of them to be clumps of star formation, all of which are found in the tail of gas. The 27 other sources are mostly background sources, such as distant galaxies.

Figure 3: Map of 37 bright sources around D100. Those labelled in blue/underlined are star-forming clumps
Credit: Cramer et al. 2019

The main conclusion of the paper is that the stripped gas can form stars outside of the galactic disc, but that it doesn’t form them uniformly throughout the tail. Instead, stars form in these clumps, which are up to 100 parsecs in size. The brightness of these regions is, however, insufficient to produce all of the Hα emission that is observed. This indicates that another mechanism (such as gas shocks) must be responsible for some of this emission, but the precise nature of this mechanism remains, for now, a mystery.

Although this paper is a convincing endorsement of ram-pressure stripping, it is important to note that ram-pressure alone is not enough to explain all of the differences between cluster and field galaxies. For example, it provides no explanation of why disc galaxies are rarer in clusters. A full description of the relationship between galaxies and their environments is likely to be a complex combination of different effects, in which ram-pressure stripping will play a small, but important, role.

Original astrobite edited by Alex Gough and Kate Storey-Fisher.

About the author, Roan Haggar: 

I’m a PhD student at the University of Nottingham, working with hydrodynamical simulations of galaxy clusters to study the evolution of infalling galaxies. I also co-manage a portable planetarium that we take round to schools in the local area. My more terrestrial hobbies include rock climbing and going to music venues that I’ve not been to before.

By Astrobites

Editor’s note: Astrobites is a graduate-student-run organization that digests astrophysical literature for undergraduate students. As part of the partnership between the AAS and astrobites, we occasionally repost astrobites content here at AAS Nova. We hope you enjoy this post from astrobites; the original can be viewed at astrobites.org. 

 

Source: American Astronomical Society (NOVA)

 

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Does the Gas in Galaxy Clusters Flow Like Honey?

Coma Cluster

Credit X-ray: NASA/CXC/Univ. of Chicago, I. Zhuravleva et al, 

Optical: SDSS Release Date June 

 JPEG (389.3 kb) - Large JPEG (1.4 MB) - Tiff (27.8 MB) - More Images

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This image represents a deep dataset of the Coma galaxy cluster obtained by NASA's Chandra X-ray Observatory. Researchers have used these data to study how the hot gas in the cluster behaves, as reported in our press release. One intriguing and important aspect to study is how much viscosity, or "stickiness," the hot gas demonstrates in these cosmic giants.

Galaxy clusters are comprised of individual galaxies, hot gas, and dark matter. The hot gas in Coma glows in X-ray light observed by Chandra. Seen as the purple and pink colors in this new composite image, the hot gas contains about six times more mass than all of the combined galaxies in the cluster. The galaxies appear as white in the optical part of the composite image from the Sloan Digital Sky Survey. (The unusual shape of the X-ray emission in the lower right is caused by the edges of the Chandra detectors being visible.)

Despite its abundance, the density of the multimillion-degree gas in Coma, which is permeated by a weak magnetic field, is so low that the particles do not interact with each other very often. Such a low-density, hot gas cannot be studied in a laboratory on Earth, and so scientists must rely on cosmic laboratories such as the one provided by the intergalactic gas in Coma.

The researchers used the Chandra data to probe whether the hot gas was smooth on the smallest scales they could detect. They found that it is not, suggesting that turbulence is present even on these relatively small scales and the viscosity is low.

Why is the viscosity of Coma's hot gas so low? One explanation is the presence of small-scale irregularities in the cluster's magnetic field. These irregularities can deflect particles in the hot gas, which is composed of electrically charged particles, mostly electrons, and protons. These deflections reduce the distance a particle can move freely and, by extension, the gas viscosity.

Knowledge of the viscosity of gas in a galaxy cluster and how easily turbulence develops helps scientists understand the effects of important phenomena such as collisions and mergers with other galaxy clusters, and galaxy groups. Turbulence generated by these powerful events can act as a source of heat, preventing the hot gas in clusters from cooling to form billions of new stars.

A paper describing this research appeared in Nature Astronomy on June 17th, 2019 and is available online. The authors of the paper are Irina Zhuravleva (University of Chicago), Eugene Churazov, (Max Planck Institute for Astrophysics in Garching and the Space Research Institute in Moscow), Alexander Schekochihin (University of Oxford), Steven Allen (Stanford University, SLAC), Alexey Vikhlinin (Harvard-Smithsonian Center for Astrophysics), and Norbert Werner (MTA-Eötvös University Lendulet, Masaryk University, Hiroshima University). NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

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Fast Facts for Coma Cluster:

Scale: Image is about 25 arcmin (2.2 million light years) across.
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 12h 59m 42s | Dec +27° 56´ 40.9"
Constellation: Coma Berenices
Observation Date: 36 pointings from March 2008 to March 2017
Observation Time: 416 hours 40 minutes (17 days 8 hours 40 minutes)

Obs. ID: 9714, 10672, 13993–13996, 14406, 14410, 14411, 14415, 18271–18276, 18761, 18791–18798, 19998, 20010, 20011, 20027–20031, 20037–20039

Instrument: ACIS
References: Zhuravleva, I. et al, 2019, Nature Astronomy, arXiv:1906.06346
Color Code: X-ray: purple; Optical: white
Distance Estimate: About 320 million light years (z=0.023)

Source: NASA’s Chandra X-ray Observatory/Press

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Hubble Uncovers Thousands of Globular Star Clusters Scattered Among Galaxies

Coma Cluster Full Mosaic

This is a Hubble Space Telescope mosaic of the immense Coma cluster of over 1,000 galaxies, located 300 million light-years from Earth. Hubble's incredible sharpness was used to do a comprehensive census of the cluster's most diminutive members: a whopping 22,426 globular star clusters. Among the earliest homesteaders of the universe, globular star clusters are snow-globe-shaped islands of several hundred thousand ancient stars. The survey found the globular clusters scattered in the space between the galaxies. They have been orphaned from their home galaxies through galaxy tidal interactions within the bustling cluster. Astronomers will use the globular cluster field for mapping the distribution of matter and dark matter in the Coma galaxy cluster.

Release Images

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Gazing across 300 million light-years into a monstrous city of galaxies, astronomers have used NASA's Hubble Space Telescope to do a comprehensive census of some of its most diminutive members: a whopping 22,426 globular star clusters found to date.

The survey, published in the November 9, 2018, issue of The Astrophysical Journal, will allow for astronomers to use the globular cluster field to map the distribution of matter and dark matter in the Coma galaxy cluster, which holds over 1,000 galaxies that are packed together.

Because globular clusters are much smaller than entire galaxies – and much more abundant – they are a much better tracer of how the fabric of space is distorted by the Coma cluster's gravity. In fact, the Coma cluster is one of the first places where observe

d gravitational anomalies were considered to be indicative of a lot of unseen mass in the universe – later to be called “dark matter.”

Among the earliest homesteaders of the universe, globular star clusters are snow-globe-shaped islands of several hundred thousand ancient stars. They are integral to the birth and growth of a galaxy. About 150 globular clusters zip around our Milky Way galaxy, and, because they contain the oldest known stars in the universe, were present in the early formative years of our galaxy.

Some of the Milky Way's globular clusters are visible to the naked eye as fuzzy-looking "stars." But at the distance of the Coma cluster, its globulars appear as dots of light even to Hubble's super-sharp vision. The survey found the globular clusters scattered in the space between the galaxies. They have been orphaned from their home galaxy due to galaxy near-collisions inside the traffic-jammed cluster. Hubble revealed that some globular clusters line up along bridge-like patterns. This is telltale evidence for interactions between galaxies where they gravitationally tug on each other like pulling taffy.

Astronomer Juan Madrid of the Australian Telescope National Facility in Sydney, Australia first thought about the distribution of globular clusters in Coma when he was examining Hubble images that show the globular clusters extending all the way to the edge of any given photograph of galaxies in the Coma cluster.

He was looking forward to more data from one of the legacy surveys of Hubble that was designed to obtain data of the entire Coma cluster, called the Coma Cluster Treasury Survey. However, halfway through the program, in 2006, Hubble's powerful Advanced Camera for Surveys (ACS) had an electronics failure. (The ACS was later repaired by astronauts during a 2009 Hubble servicing mission.)

To fill in the survey gaps, Madrid and his team painstakingly pulled numerous Hubble images of the galaxy cluster taken from different Hubble observing programs. These are stored in the Space Telescope Science Institute's Mikulski Archive for Space Telescopes in Baltimore, Maryland. He assembled a mosaic of the central region of the cluster, working with students from the National Science Foundation's Research Experience for Undergraduates program. "This program gives an opportunity to students enrolled in universities with little or no astronomy to gain experience in the field," Madrid said.

The team developed algorithms to sift through the Coma mosaic images that contain at least 100,000 potential sources. The program used globular clusters' color (dominated by the glow of aging red stars) and spherical shape to eliminate extraneous objects – mostly background galaxies unassociated with the Coma cluster.

Though Hubble has superb detectors with unmatched sensitivity and resolution, their main drawback is that they have tiny fields of view. "One of the cool aspects of our research is that it showcases the amazing science that will be possible with NASA's planned Wide Field Infrared Survey Telescope (WFIRST) that will have a much larger field of view than Hubble," said Madrid. "We will be able to image entire galaxy clusters at once."

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

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Credits:

Image: NASA, ESA, J. Mack (STScI), and J. Madrid (Australian Telescope National Facility)

Science: NASA, ESA, and J. Madrid (Australian Telescope National Facility)

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Related Links

• This site is not responsible for content found on external linksNASA's Hubble Portal
• The science paper by J. Madrid et al.

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Contact

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu

Juan Madrid
Australian Telescope National Facility, Sydney, Australia
jmadrid@astro.swin.edu.au

Source: HubbleSite/News

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The sleeping giant

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The sleeping giant NGC 4889

 

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Wide-field view of NGC 4889 (ground-based view)

Videos

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Zooming onto the galaxy NGC 4889

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Panning across the elliptical galaxy NGC 4889

The placid appearance of NGC 4889 can fool the unsuspecting observer. But the elliptical galaxy, pictured in this new image from the NASA/ESA Hubble Space Telescope, harbours a dark secret. At its heart lurks one of the most massive black holes ever discovered.

Located about 300 million light-years away in the Coma Cluster, the giant elliptical galaxy NGC 4889, the brightest and largest galaxy in this image, is home to a record-breaking supermassive black hole. Twenty-one billion times the mass of the Sun, this black hole has an event horizon — the surface at which even light cannot escape its gravitational grasp — with a diameter of approximately 130 billion kilometres. This is about 15 times the diameter of Neptune’s orbit from the Sun. By comparison, the supermassive black hole at the centre of our galaxy, the Milky Way, is believed to have a mass about four million times that of the Sun and an event horizon just one fifth the orbit of Mercury.

But the time when NGC 4889’s black hole was swallowing stars and devouring dust is past. Astronomers believe that the gigantic black hole has stopped feeding, and is currently resting after feasting on NGC 4889’s cosmic cuisine. The environment within the galaxy is now so peaceful that stars are forming from its remaining gas and orbiting undisturbed around the black hole.

When it was active, NGC 4889’s supermassive black hole was fuelled by the process of hot accretion. 

When galactic material — such as gas, dust and other debris — slowly fell inwards towards the black hole, it accumulated and formed an accretion disc. Orbiting the black hole, this spinning disc of material was accelerated by the black hole’s immense gravitational pull and heated to millions of degrees. This heated material also expelled gigantic and very energetic jets. During its active period, astronomers would have classified NGC 4889 as a quasar and the disc around the supermassive black hole would have emitted up to a thousand times the energy output of the Milky Way.

The accretion disc sustained the supermassive black hole’s appetite until the nearby supply of galactic material was exhausted. Now, napping quietly as it waits for its next celestial snack, the supermassive black hole is dormant. However its existence allows astronomers to further their knowledge of how and where quasars, these still mysterious and elusive objects, formed in the early days of the Universe.

Although it is impossible to directly observe a black hole — as light cannot escape its gravitational pull — its mass can be indirectly determined. Using instruments on the Keck II Observatory and Gemini North Telescope, astronomers measured the velocity of the stars moving around NGC 4889’s centre. These velocities — which depend on the mass of the object they orbit — revealed the immense mass of the supermassive black hole.

More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image credit: NASA & ESA

Links

• Images of Hubble

Contacts:

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching bei München, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

Source: ESA/HUBBLE /News 

Astronomers Discover More than 800 Dark Galaxies in the Famous Coma Cluster

Figure 1: A color image made with B, R, and i-band images from the Subaru Telescope. A small region of 6 x 6 arcmin is cut out from large Coma Cluster images. Yellow circles show two of the 47 dark galaxies discovered last year, and green circles are the ones discovered in this new study. Image without the labels is here, image without the labels and circles is here. (Credit: NAOJ) 

Figure 2: A 2.9 x 2.9 degree field-of-view sky image of the Coma Cluster.

(Left) An image from the Digitized Sky Survey (from a digitized photo-plate). Eighteen white squares are the coverage by the Subaru Telescope with the R-band filter. Red and yellow parts were observed in multiple bands with Subaru, which enabled the study of galaxy colors. The light blue region is the area in Figure 1.

(Right) The distribution of the newly found dark galaxies. Blue circles indicate the ones of particularly large sizes (roughly the size of the Milky Way galaxy even though the total light is only 1/1,000 of the Milky Way). (Credit: NAOJ/Stony Brook University)

A group of researchers from the Stony Brook University (the State University of New York) and the National Astronomical Observatory of Japan has discovered 854 "ultra dark galaxies" in the Coma Cluster by analyzing archival data from the Subaru Telescope. The discovery of 47 such mysterious dark galaxies was a surprising find in 2014, and the new discovery of more than 800 suggests galaxy clusters as the key environment for the evolution of these mysterious dark galaxies. "Not only these galaxies appear very diffuse," said Jin Koda, principal investigator of the study, "but they are very likely enveloped by something very massive." 

These galaxies appear very diffuse and remarkably extended as seen by the light of the stars they contain. Many are similar in size to the Milky Way, but have only 1/1,000 of stars that our galaxy does (Figure 1). The stellar population within such fluffy extended galaxies is subject to rapid disruption due to a strong tidal force detected within the cluster. Something invisible must be protecting the fragile star systems of these galaxies, something with a high mass. That "something" is very likely an excessive amount of dark matter. The component of visible matter, such as stars, is calculated to contribute only 1% or less to the total mass of each galaxy. The rest – dark matter – accounts for more than 99%.

The Subaru Telescope, with its large-aperture and wide-field camera, used under excellent seeing conditions, revealed that these dark galaxies contain old stellar populations and shows a spatial distribution similar to those of other brighter galaxies in the Coma Cluster (Figure 2). That suggests they have been a long-lived population of galaxies within the cluster. The amount of visible matter they contain, less than 1%, is extremely low compared to the average fraction within the universe. 

Why are these galaxies dark? Somehow, they lost gas needed to create new stars during or after their largely unknown formation process billions of years ago. From their preferential presence within the cluster, it’s likely that the cluster environment played a key role in the loss of gas, which affects star formation within the galaxy. Several loss mechanisms are possible, including ram-pressure stripping by intra-cluster gas, gravitational interactions with other galaxies within the cluster, and gas outflows due to simultaneous supernova explosions triggered, e.g., by the ram pressure or gravitational encounters.

These dark galaxies may offer another insight into the model of galaxy formation. However, according to Dr. Jin Koda more work needs to be done to understand them and their place in the standard picture of galaxy formation. "Follow-up spectroscopic observations in the future may reveal the history of star formation in these dark galaxies," he said.

In addition to research into galaxies’ stellar populations, further investigation of the large dark matter component of the galaxies is essential. Dark matter is invisible, but measurements of stellar motions may expose the distribution of dark matter in these galaxies. Such a dream measurement may not be immediately possible, because they are so faint. It is difficult to measure the detailed motions of stars, even with the Subaru Telescope. The construction of Thirty Meter Telescope (TMT) by an international partnership of institutions, including the National Astronomical Observatory of Japan may well reveal the mystery of the dark galaxies in near future.

The National Astronomical Observatory of Japan has maintained all the data obtained with the Subaru Telescope since its very first light observations 16 years ago (in 1999). All archive data are made available to the community one and half years from the night of the observation. This new discovery is made possible thanks to the availability of abundant archival Subaru data. Re-analyses of archival data have often resulted in new discoveries and publications. The Subaru data archive continuously offers "treasure hunting" opportunities

This discovery will be published on June 24, 2015 in the Astrophysical Journal Letters by the American Astronomical Society (Koda et al. 2015, "Approximately A Thousand Ultra Diffuse Galaxies in the Coma cluster"). The preprint is available here.

Team members

• Jin Koda (Stony Brook University)
• Masafumi Yagi (National Astronomical Observatory of Japan/Hosei University)
• Hitomi Yamanoi (National Astronomical Observatory of Japan)
• Yutaka Komiyama (National Astronomical Observatory of Japan/SOKENDAI - the Graduate University for Advanced Studies)

Source: Subaru Telescope

Measuring gas velocities in galaxy clusters with X-ray images

Fig 1: Schematic illustration of gas density distribution in a spherically symmetric cluster in perfect hydrostatic equilibrium (v=0, top) and in a slightly disturbed cluster (v ≠ 0, middle). Slow large-scale perturbations in a stratified cluster atmosphere can be interpreted as internal waves (as illustrated in the bottom panel), similar to waves in the ocean, where the velocity of water and the amplitude of waves are linked. In clusters, similar perturbations are caused by a variety of reasons, including minor mergers or the activity of the central supermassive black holes.

Fig 2: X-ray image of the Coma cluster as seen with Chandra observatory.

The substructure seen in the image implies that the X-ray emitting gas is not at rest. 

X-ray observations provide us with detailed information on the density and temperature of the hot gas inside galaxy clusters. The other major gas characteristic that still needs to be measured is the gas velocity. While current generation X-ray observatories lack the required energy resolution to measure velocities directly, future observatories such as ASTRO-H and ATHENA will address this limitation.

An international team including MPA scientists has shown that the power spectrum of the velocity field can inferred indirectly from existing X-ray images of relaxed clusters. Numerical simulations confirm this simple theoretical idea, opening a way of probing gas velocities using already existing X-ray data. 

Galaxy clusters are the largest gravitationally bound structures in the present Universe. Hot gas (with temperatures of 10 to 100 million Kelvin) fills their gravitational potential wells and shines in the X-ray band, making the clusters an easy target for orbital X-ray observatories. Both the density and the temperature of the gas in clusters is routinely measured using X-ray data, while it is notoriously difficult to directly measure the turbulent motion of the gas via the Doppler shift of X-ray lines. Since the information on the turbulent gas velocities would have profound implications for the mass determination of clusters and for determining the plasma microphysics, new approaches have been developed to indirectly measure the gas velocities using existing X-ray data. One of these approaches is based on the analysis of small-scale fluctuations in X-ray images as described below. 

In relaxed clusters the gas approaches the state of hydrostatic equilibrium, when all thermodynamic properties are aligned along surfaces with equal gravitational potential, making X-ray images smooth and round (see Fig.1). These stratified and stable atmospheres of cluster gas bear much similarity to the Earth's atmosphere or to water in the oceans where cold and dense material tends to be below hotter and lighter material due to the combined action of gravity and buoyancy. Slow subsonic perturbations of such atmospheres can be represented as a combination of internal (gravity) waves, very much like waves in the ocean (bottom panel of Fig.1). In oceans there is a simple relation: the larger the amplitude of the waves, the higher the velocity of water. Is the same true for gas in galaxy clusters? Both theoretical analysis and numerical simulations have shown that this is indeed the case.

The main idea is that gas is disturbed on large scales and that this results in a cascade of waves. In clusters these waves are creating perturbations in the gas density that are visible in X-ray images as small-scale fluctuations of the surface brightness relative to a smooth global model. Our analysis shows that there is a simple linear relation between the gas velocities and density perturbations. Moreover, this relation holds for a broad range of scales: on large scales, where buoyancy effects dominate (internal waves), as well as on small scales where the isotropic turbulent cascade usually develops. At these small scales, the entropy of the gas acts as a passive scalar advected by the velocity field and makes the gas displacement visible in X-rays. 

Based on these arguments one can expect that in relaxed clusters (i.e. clusters which are only slightly disturbed) the power spectrum of the velocity field can simply be recovered from the power spectrum of density fluctuations. The latter can be straightforwardly estimated from X-ray images. 

Numerical simulations (cosmological simulations of cluster formation and pure hydrodynamic simulations with turbulence) confirm this conclusion and open an interesting possibility to use gas density power spectra as a proxy for the velocity power spectra in relaxed clusters. 

Once the gas velocities can be measured directly with future X-ray observatories, it will be possible to push this analysis further and search for differences between the density and velocity power spectra. Strong departures of the two power spectra from the universal behavior described above can then be used to constrain physical effects such as conductivity or viscosity in the gas.

Eugene Churazov (MPA), Massimo Gaspari (MPA), Irina Zhuravleva (Stanford), Alex Schekochihin (Oxford), Rashid Sunyaev (MPA)

References:
 

Zhuravleva I., Churazov E., Schekochihin A. A., Lau E. T., Nagai D., Gaspari  M., Allen S. W., Nelson K., Parrish I. J., The Relation between Gas Density and Velocity Power Spectra in Galaxy Clusters: Qualitative Treatment and Cosmological Simulations, 2014, ApJL, 788, 13

 

Gaspari M., Churazov E., Nagai D., Lau E. T., Zhuravleva, I., The relation between gas density and velocity power spectra in galaxy clusters: high-resolution hydrodynamic simulations and the role of conduction,2014, A&A, 569A, 67

 

Gaspari M., Churazov E., Constraining turbulence and conduction in the hot ICM through density perturbations, 2013, A&A, 559A, 78

 

Churazov E.; Vikhlinin A.; Zhuravleva I.; Schekochihin A.; Parrish I.; Sunyaev R.; Forman W.; Böhringer H.; Randall S., X-ray surface brightness and gas density fluctuations in the Coma cluster, 2012, MNRAS, 421,1123

Source:  Max Planck Institute for Astrophysics