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Abell 2597 Animations
Click for low-resolution animation
Tour of Abell 2597
Quicktime MPEG With closed-captions (at YouTube)

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]

(Credit: NASA/CXC/A. Hobart)

Click for low-resolution animation
Weather Forecast Predicts Rain Around Black Holes
Quicktime MPEG With closed-captions (at YouTube)

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]

(Credit: NASA/CXC/April Jubett)

Return to Abell 2597 (March 4, 2015)