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Groups & Clusters of Galaxies
X-ray Astronomy Field Guide
Groups & Clusters of Galaxies
Questions and Answers
Groups & Clusters of Galaxies
Chandra Images
Groups & Clusters of Galaxies
Animations & Video: Groups & Clusters of Galaxies
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1. 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.
[Runtime: 01:49]
(NASA/CXC/A. Hobart)

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2. Tour of Abell 2597
QuicktimeMPEG Astronomers have known for quite some time that supermassive black holes influence the growth of galaxies they live in, but they have been trying to figure out exactly how. A new study of over 200 galaxy clusters using data from NASA's Chandra X-ray Observatory is an important step in that direction. Researchers used Chandra to look at some of the largest known galaxies lying in the middle of galaxy clusters. These galaxies are embedded in enormous atmospheres of hot gas. This hot gas should cool and many stars should then form. However, observations show that something is hindering the star birth. The latest study suggests that a phenomenon referred to as cosmic precipitation may be playing a critical role. Cosmic precipitation is not rain, sleet, or snow. Rather, it is a mechanism that allows hot gas to produce showers of cool gas clouds that fall into a galaxy. Some of these clouds form stars, but others rain onto the supermassive black hole, triggering jets of energetic particles that push against the falling gas and reheat it. This prevents more stars from forming. This cycle of cooling and heating creates a feedback loop that regulates the growth of the galaxies. Future studies will test whether this precipitation-black hole feedback process also regulates star formation in smaller galaxies, including our own Milky Way galaxy.
[Runtime: 01:56]
(NASA/CXC/April Jubett)

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3. Tour of il Gioiello Cluster
QuicktimeMPEG Galaxy clusters are the largest structures in the Universe held together by gravity. Because of their immense size, their growth and evolution tell us a lot about how the Universe itself has changed over time. A newly discovered galaxy cluster provides some intriguing clues. This galaxy cluster is officially known as XDCP J0044.0-2033. Perhaps not surprisingly, astronomers decided to give a nickname to this mouthful of a cluster name. Because this cluster has many colors in X-ray light due to its plentiful hot gas and star forming galaxies, astronomers dubbed this the “Gioiello” Cluster, which means “Jewel” in Italian. The Gioiello Cluster is located about 9.6 billion light years from Earth. Scientists think this cluster formed approximately 3.3 billion years after the Big Bang. This means that the Gioiello Cluster is a mere 800 million years old as we observe it. A long observation from Chandra, totally over four days worth of observing time, provided astronomers with enough information to accurately determine the mass and other properties of the cluster. They found the Gioiello Cluster tops out at a whopping 400 trillion times the mass of the Sun. The discoveries of the Gioiello Cluster and others like it are helping astronomers better understand how galaxy clusters have developed over the lifetime of the Universe.
[Runtime: 01:56]
(NASA/CXC/A. Hobart)

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4. Please Don't Stop the Music!
QuicktimeMPEG Did you know that the sounds we hear on Earth are just vibrations of air? But that doesn't mean that space is an eerily silent place, just because there isn't any air out there. This is because air is a collection of gases, and there are clouds of gas in space that can vibrate and allow sound to travel too.

Okay, so we know how sound can travel in space, but what's making all of the noise? The answer is powerful objects that give off huge amounts of energy - enough to make the gases vibrate.

For example, in addition to gobbling up material, black holes also release powerful jets of energy. Astronomers already know that the black hole at the centre of a collection of galaxies called the Perseus Cluster is powerful enough to make a very deep sound.

"We thought that these very deep sounds might be found in galaxy clusters everywhere," says astronomer Ryan Foley. However, Ryan is a member of a team of astronomers who have recently observed a galaxy cluster called the Phoenix Cluster (shown in the photo above) that is practically totally silent. This means that either not all galaxy clusters produce sound, or that sometimes the music almost completely stops!
[Runtime: 01:47]
(NASA/CXC/A. Hobart)

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5. Tour of Perseus Cluster and Virgo Cluster
QuicktimeMPEG Galaxy clusters are enormous. In fact, they are the largest objects in the Universe held together by gravity. Just one galaxy cluster can contain hundreds or even thousands of individual galaxies. And what may be more interesting is that these galaxies make up just a fraction of the mass in these clusters. In addition to dark matter, the bulk of the mass in clusters actually comes from vast amounts of very thin gas. This gas is so hot that it only reveals itself in X-ray light. For many years, scientists have wondered why the hot gas doesn't cool and form lots of stars. With Chandra, astronomers have looked at many galaxy clusters, and in some, they found giant cavities carved out of the hot gas. They realized that the supermassive black holes at the centers of these clusters were pumping energy out into the gas through powerful jets. Now researchers have direct evidence for just how that energy keeps the gas in the entire galaxy cluster so hot. The answer may be turbulence. The same phenomenon that causes a bumpy airplane ride also prevents the hot gas in these galaxy clusters from ever settling down enough to cool. So while there are still many new things to learn about galaxy clusters, scientists may be finally homing in on the answer to one question that they have been asking for decades.
[Runtime: 01:35]
(NASA/CXC/A. Hobart)

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6. Archaeologists of the Universe
QuicktimeMPEG Astronomers and archaeologists (like Indiana Jones) have a lot in common, as they both look for clues to understand past events. However, while archaeologists have to dig deep underground to find fossils and ruins, all astronomers have to do is look up to the night sky. That's because when we look at objects in the night sky, we are seeing them as they looked when the light they gave off started its long journey across the Universe to us!

This means that each view of the Universe reveals a snapshot of the Universe's history. Take this new picture, for example. It shows the aftermath of a collision between two huge groups of galaxies, which are called galaxy clusters. Following the collision, the galaxy clusters joined together to form what is now called the Musket Ball Cluster. In the picture, astronomers have colored some parts blue and pink to show where different types of material are found.

This isn't the first time that astronomers have spotted a collision of galaxy clusters. However, they only gave astronomers a snapshot of the aftermath of these collisions about 200 million years after impact. But this picture of the Musket Ball Cluster was taken about 700 million years after the collision.

This will give astronomers important clues about the long-term effects of such huge collisions. For example, astronomers still don't know if the collision of galaxy clusters will help or prevent new stars from forming, or if they have little effect.
[Runtime: 02:05]
(NASA/CXC/April Jubett)

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7. Tour of Perseus Cluster
QuicktimeMPEG A team of astronomers has used NASA's Chandra X-ray Observatory and ESA's XMM-Newton to study a large group of galaxy clusters with a surprising result. Galaxy clusters are the largest objects in the Universe held together by gravity, and thus can reveal lots of information about the cosmos. This most recent study, which included the well-known Perseus cluster and 72 others, has uncovered a mysterious X-ray signal. Astronomers are intrigued by a spike of intensity at a specific wavelength of X-ray light in the data because of one proposed explanation. Scientists think that a hypothetical particle called a sterile neutrino may, in fact, be responsible for this spike of intensity. Some scientists have proposed that the sterile neutrino could be a candidate for dark matter, something that makes up about 85% of the Universe yet does not emit or absorb light. While they are excited about this finding, the researchers say it's too early to claim whether or not this mysterious X-ray signal is real, or whether or not it is indeed the signature of the sterile neutrino. They'll keep gathering data and looking at other galaxy clusters to make sure they see it elsewhere. In the meantime, they'll be looking at their theories to see where else the physics may take them.
[Runtime: 01:40]
(NASA/CXC/A. Hobart)

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8. Collecting Clues to a Cosmic Crime
QuicktimeMPEG Picture the scene: you're in the countryside far from the nearest village, on a warm summer night. The wind is still and there's silence except for the soft sounds of night-time animals. You lie on your blanket among the long green grass and gaze up at the clear night sky. The moon smiles down at you and the stars twinkle happily. Can you imagine a time you've ever felt so relaxed?

But everything is not as it seems. Deep in space there is a spiral galaxy being violently ripped apart by its neighbors!

The galaxy is called ESO 137-001 and in reality it is hidden from our view by a thick fog of space dust. You can only see it in this photograph thanks to the impressive power of the Hubble Space Telescope and the Chandra X-ray Observatory.

ESO 137-001 is travelling through the heart of a cluster of galaxies called Abell 3627. As it moves, the pull of the surrounding galaxies is tearing at it from all sides. Bright blue streaks are being torn from it, leaving behind tell-tale clues to this cosmic crime. Upon closer inspection, these blue streaks are rows of hot, bright, young stars.

ESO 137-001 is part of the Norma Cluster, a cluster of galaxies near the center of the Great Attractor. We're not exactly certain what The Great Attractor is, but it definitely earns its name! The region is so massive and has a gravitational pull so strong, that it is pulling entire galaxy clusters toward it! Even our Galaxy is being slowly dragged toward this mysterious part of space.
[Runtime: 02:23]
(NASA/CXC/April Jubett)

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9. Growth of the Coma Colossus
QuicktimeMPEG This picture shows the very large, very distant and very gassy Coma Cluster. It's a giant cluster of over 1000 galaxies that are all bound together by gravity. If you take a close look, you can make out the yellow-white shapes of galaxies scattered across the picture. The pink blobs show arms of multi-million degree gas, hot enough to cook your lungs in half a breath.

All big clusters of galaxies contain this very hot gas. The gas sends out lots of powerful X-rays because it's so hot, and these are what we can see in pink here. You can't see X-rays with your eyes, so astronomers have coloured them in pink. This gas is actually a very helpful tool for us, because the amount of material in the cluster can be measured using just the temperature of the gas! The hotter the gas, the more material there is!

Our Galaxy is also part of a group of galaxies, called the Local Group. Our cluster is also filled with gas, but it's so spread out that we don't see it when we look into the night sky. And because the Local Group is much smaller than the Coma Cluster, the gas around our galaxy isn't nearly as hot.

The gas in this picture also tells another story. The shape of these pink clouds and how they are spread throughout the cluster give us clues into how the Coma Cluster has grown. They show us that smaller groups of galaxies and smaller galaxy clusters have crashed and combined over time. The final result is the colossal Coma Cluster we see today, one of the biggest structures in the entire Universe!
[Runtime: 02:07]
(NASA/CXC/April Jubett)

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10. Tour of Coma Cluster
QuicktimeMPEG Galaxy clusters are the largest structures in the Universe held together by gravity. Because they are so big, they play a very important role in the Universe. A new result is revealing clues to how these giant structures grow and evolve over time. Astronomers have discovered enormous arms of hot gas in the Coma cluster of galaxies by using Chandra X-ray Observatory and XMM-Newton, another orbiting X-ray observatory run by the European Space Agency. Researchers think that these arms were most likely formed when smaller galaxy clusters had their gas stripped away by the head wind created by the motion of the clusters through the hot gas -- much the same way that the headwind created by a roller coaster blows the hats off riders. By studying these remarkable arms that span over a half a million light years across, astronomers are taking another step toward understanding the past, present, and perhaps future of these colossal objects.
[Runtime: 01:03]
(NASA/CXC/A. Hobart)

Related Chandra Images: