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Groups & Clusters of Galaxies
X-ray Astronomy Field Guide
Groups & Clusters of Galaxies
Questions and Answers
Groups & Clusters of Galaxies
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Groups & Clusters of Galaxies
Animations & Video: Groups & Clusters of Galaxies
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1. Tour of Galaxy Clusters
QuicktimeMPEG Since its discovery almost two decades ago, dark energy has remained one of the biggest mysteries in science. Astronomers know that dark energy is responsible for the current accelerating expansion of the Universe, but they are still trying to determine just what it is.

A new study tries to tackle the questions surrounding dark energy by examining properties of X-ray emission from galaxy clusters. Galaxy clusters are the largest structures in the Universe held together by gravity and they contain enormous amounts of hot gas that glow in X-ray light. Researchers know that galaxy clusters possess another interesting quality: the more massive ones are simply scaled up versions of the smaller ones -- like Russian dolls that fit inside one another.

Astronomers can take advantage of this fact to use galaxy clusters as cosmic distance markers. Since dark energy is pushing the Universe apart, the different distances of these galaxy clusters reveals clues about the nature of dark energy itself.

The latest research, looking at over 300 galaxy clusters, shows that dark energy does not appear to change over billions of years. This supports the idea that dark energy is what Einstein called the cosmological constant, which is the equivalent to the energy of empty space. While this new study is very exciting, there is still much to be learned before we know exactly what dark energy is, how it has affected the Universe in the past, and what it might do in the future.
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(NASA/CXC/A. Hobart)

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2. Tour of Frontier Fields
QuicktimeMPEG Galaxy clusters are enormous collections of hundreds or even thousands of galaxies and vast reservoirs of hot gas embedded in massive clouds of dark matter. These cosmic giants are not merely novelties of size or girth. Instead, they represent pathways to understanding how our entire universe evolved in the past and where it may be heading in the future.

To learn more about galaxy clusters, including how they grow via collisions, astronomers have collected large quantities of data from some of the world's most powerful telescopes. They have used telescopes that detect different kinds of light to study a half dozen galaxy clusters in depth. The name for this galaxy cluster project is the "Frontier Fields".

Two of these Frontier Fields galaxy clusters, going by their abbreviated names, are MACS J0416 and MACS J0717. Located about 4.3 billion light years from Earth, MACS J0416 is a pair of colliding galaxy clusters that will eventually combine to form an even bigger cluster. MACS J0717, one of the most complex and distorted galaxy clusters known, is the site of a collision between four clusters. It is located about 5.4 billion light years away from Earth.

In the new Frontier Fields studies, astronomers combined data from NASA's Chandra X-ray Observatory and Hubble Space Telescope along with information in radio waves from the NSF's Very Large Array and the Giant Metrewave Radio Telescope in India. They have found new details about both of these complex and colliding systems. Astronomers will continue to analyze the vast amounts of data from the Frontier Fields, which will help them learn more about these gigantic and important objects.
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(NASA/CXC/A. Hobart)

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3. A Tour of IDCS J1426.5+3508
QuicktimeMPEG How quickly can galaxy clusters - the Universe's largest objects held together by gravity - form? Astronomers don't know exactly, but by examining some of these mega-structures in the early Universe they can begin to figure it out. The galaxy cluster called IDCS J1426.5+3508 is one that helps astronomers do just that. This galaxy cluster was first discovered by the Spitzer Space Telescope in 2012. Follow-on observations by the Hubble Space Telescope and the Keck Observatory in Hawaii pinpointed its distance. Radio data from the CARMA telescope array in California then suggested this galaxy cluster was very massive. New X-ray data from Chandra confirmed that IDCS J1426 was indeed enormous, weighing in at a whopping 500 trillion times the mass of our Sun. This is the most massive galaxy cluster discovered at this epoch in the early Universe - just 3.8 billion light years after the Big Bang. While this sounds like an incredibly long time, it is relatively quick in terms of forming something the size of IDCS J1426. By studying this galaxy cluster, astronomers hope to better understand how these colossal objects formed and evolved in the young Universe.
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(NASA/CXC/A. Hobart)

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4. A Tour of Zwicky 8338
QuicktimeMPEG An extraordinary ribbon of hot gas trailing behind a galaxy like a tail has been discovered using data from NASA's Chandra X-ray Observatory. This ribbon, or X-ray tail, is likely due to gas stripped from the galaxy as it moves through a vast cloud of hot intergalactic gas. With a length of at least 250,000 light years, it is likely the largest such tail ever detected.

The tail is located in the galaxy cluster Zwicky 8338, which is almost 700 million light years from Earth. The length of the tail is more than twice the diameter of the entire Milky Way galaxy and contains gas with temperatures of about 10 million degrees.

Galaxy clusters are the largest structures in the Universe held together by gravity. They consist of hundreds, or even thousands, of galaxies, enormous pools of hot gas, and vast amounts of unseen dark matter. Since galaxy clusters are so enormous, they play a critical role inunderstanding how our Universe evolves. X-ray tails like the one in Zwicky 8338 show how the galaxies within a cluster can transform over time. This gives scientists important information in understanding these critical cosmic systems.
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(NASA/CXC/A. Hobart)

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5. Tour of SDSS J103842.59+484917.7
QuicktimeMPEG One hundred years ago this month, Albert Einstein published his theory of general relativity, one of the most important scientific achievements in the last century. A key result of Einstein's theory is that matter warps space-time. This means that a massive object can bend the light we see on Earth from very distant objects, say, faraway galaxies. Astronomers have found many examples of this phenomenon, known as "gravitational lensing." Gravitational lensing is more than just a cosmic illusion, however. Instead, gravitational lensing provides astronomers with a way of probing extremely distant galaxies and groups of galaxies in ways that would otherwise be impossible even with the most powerful telescopes.

The latest results from the "Cheshire Cat" group of galaxies show how manifestations of Einstein's 100-year-old theory can lead to new discoveries today. Astronomers have given the group this name because to many it looks like a smiling cat from the famous story of "Alice in Wonderland." In a twist that perhaps Lewis Carroll could appreciate, some of the feline features in this cosmic Cheshire Cat are actually distant galaxies whose light has been stretched and bent by the large amounts of mass in the system.

Astronomers have studied the Cheshire Cat in optical light from telescopes like the Hubble Space Telescope and the Gemini Observatory on Mauna Kea. They have also used the Chandra X-ray Observatory to study it in higher-energy light. X-rays from Chandra reveal gas in between the galaxies that has been heated to millions of degrees. This superhot gas is evidence that the two eyes of the Cheshire Cat, and the small galaxies associated with them, are racing toward one another at very high speeds. In fact, astronomers estimate that these galaxies will merge in about one billion years. X-ray data also show that the left "eye" of the Cheshire Cat group contains an actively feeding supermassive black hole at the center of the galaxy. Scientists will continue to study this system and others like it to explore all of the ways Einstein's theory from a century ago helps explain our view of the Universe today.
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(NASA/CXC/A. Hobart)

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6. Banking X-ray Data for the Future
QuicktimeMPEG Archives, in their many forms, save information from today that people will want to access and study in the future. This is a critical function of all archives, but it is especially important when it comes to storing data from today's modern telescopes.

NASA's Chandra X-ray Observatory has collected data for over sixteen years on thousands of different objects throughout the Universe. The science team has immediate access to the data, and then a year after observation all of the data goes into a public archive where it can be folded into later studies.

To celebrate October being American Archive Month a collection of images from the Chandra archive is being released. Some of these objects may be familiar to readers, while others may be unknown. None of these images, in the exact form, has been released before.

By combining data from different observation dates, new perspectives of cosmic objects can be created. With archives like those from Chandra and other major observatories, such vistas will be available for future exploration.
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(NASA/CXC/A. Hobart)

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7. Tour of Phoenix Cluster
QuicktimeMPEG In 2012, astronomers announced the discovery of an extraordinary object. This galaxy cluster, which was found about 5.7 billion light years from Earth, shattered several important astronomical records. For example, it had the highest rate of cooling hot gas and star formation ever seen in the center of a galaxy cluster. Chandra observations also showed that it was the most powerful producer of X-rays of all known clusters. And, the rate at which hot gas is cooling in the center of the cluster was also the largest ever observed. The astronomers that found it nicknamed this system the Phoenix Cluster because it was found in the constellation of the Phoenix, and some of its behaviors resembled a galaxy cluster being brought back to life through new star formation.

Three years later, astronomers have gathered even more data on the Phoenix Cluster in X-ray, optical and ultraviolet light. These new observations have helped astronomers better understand what's happening in this object. They see holes, or cavities, in the X-ray data from Chandra that are surrounded by massive filaments of gas and dust. The combination of the X-ray cavities with the filaments may be responsible for the ultra-high rate of new stars forming in the Phoenix Cluster. Overall, the extreme properties of the Phoenix cluster system are providing new insights into various astrophysical problems, including the formation of stars, the growth of galaxies and black holes, and the co-evolution of black holes and their environment.
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(NASA/CXC/A. Hobart)

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8. Tour of Abell 1033
QuicktimeMPEG Galaxy clusters are the largest structures in the Universe held together by gravity. They consist of huge reservoirs of hot gas that glow in X-ray light as well as hundreds or even thousands of individual galaxies, plus unseen dark matter. Understanding how clusters grow is critical to tracking how the Universe itself evolves over time.

A new result involving the system named Abell 1033 is providing another piece to this astronomical puzzle. Located about 1.6 billion light years from Earth, Abell 1033 is the site of the collision of two galaxy clusters. By combining X-ray data from Chandra along with radio and optical data, astronomers have found evidence that Abell 1033 is what is called a "radio phoenix." What does this mean? Astronomers think a supermassive black hole close to the center of Abell 1033 underwent an eruption in the past. Streams of high-energy electrons filled a region hundreds of thousands of light years across and produced a cloud of bright radio emission. This cloud faded over a period of millions of years as the electrons lost energy and the cloud expanded.

The radio phoenix emerged when another cluster of galaxies slammed into the original cluster, sending shock waves through the system. These shock waves, similar to sonic booms produced by supersonic jets, passed through the dormant cloud of electrons. The shock waves compressed the cloud and re-energized the electrons, which caused the cloud to once again shine at radio frequencies. Just as the phoenix rises from its ashes in the stories of mythology, so too does it appear Abell 1033 has undergone an amazing rebirth.
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(NASA/CXC/A. Hobart)

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9. Tour of NGC 5813
QuicktimeMPEG Galaxy groups are families of galaxies that are bound together by gravity. They are very similar to their larger cousins, galaxy clusters. Instead of containing hundreds or even thousands of galaxies like clusters do, galaxy groups are typically comprised of 50 or fewer galaxies. Like galaxy clusters, groups of galaxies are enveloped by giant amounts of hot gas that emit X-rays. They also often contain a giant black hole at their center that can impact what's happening throughout the group.

Astronomers used NASA's Chandra X-ray Observatory to study this in the galaxy group NGC 5813, which is located about 105 million light years from Earth. They found three pairs of cavities, or bubbles, that have been carved into the hot gas. These cavities were produced by jets of material that blasted out of the central black hole, including multiple eruptions that lasted for some 50 million years. Similar to how air bubbles will rise to the surface of water, these cavities have moved away from the galaxy group's center toward the edge of the hot gas. By studying the details of these cavities, astronomers can get a better understanding of just how supermassive black holes affect their cosmic surroundings.
[Runtime: 01:35]
(NASA/CXC/A. Hobart)

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10. Weather Forecast Predicts Rain Around Black Holes
QuicktimeMPEG On Earth, precipitation happens when water is heated by the Sun and forms steam (like the steam you see rises from a kettle as the water boils). The steam rises up into the air where it cools down, reforming into tiny droplets of water. These water droplets group together and create the clouds we see in the sky.

Sometimes, something similar happens in galaxies. Clouds of hot cosmic gas cool down, becoming clouds of cold cosmic gas instead. This is also called precipitation. Can you see how the two processes are similar?

However, while precipitation on Earth allows planets and animals to grow, precipitation actually stops the growth of galaxies. At least, it does if the galaxy has a giant black hole at its center.

This is because stars are born from cold clouds of cosmic gas. But in galaxies with central black holes, when a cloud cools down, it is an easier target for a black hole to capture and feed on.

As the black hole feeds it releases a hot jet of energy. The jet then re-heats any nearby clouds of cold gas before they have chance to form into stars.
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(NASA/CXC/A. Hobart)

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