Cosmic Showers

Data from NASA’s Chandra X-ray Observatory shows that the growth of galaxies that include supermassive black holes can be inhibited by cosmic precipitation.

Cosmic precipitation is a process that allows hot gas to produce showers of cool gas clouds that fall into a galaxy.

The Chandra X-ray Observatory is looking at galaxies lying in the middle of galaxy clusters that are entrenched in giant atmospheres of hot gas. Scientists expect that when the hot gas cools stars will form. Instead, surveillance from the Chandra Observatory discovered that something is inhibiting the birth of stars.

Researchers believe that the lack of star births is due to supermassive black holes at the centers of large galaxies. They suggest that clumps of gas radiate away their energy and form cool clouds that mix with surrounding hot gas. Some of these clouds form stars, but others rain onto the supermassive black hole. This triggers jets of energetic particles that push against the falling gas and reheat it, preventing stars from forming.  The cycle of cooling and heating creates a feedback loop that regulates galaxy growth.

Using data from Chandra researchers can estimate how long it should take for the gas to cool at different distances from the black hole and predict the “weather” around each black hole.

They found that the precipitation feedback loop, driven by energy produced by the black hole jets, prevents the showers of cold clouds from getting too strong. The data suggests that the regulation of this precipitation has been going on for the last 7 billion years or more.

So a rain of cool clouds appears to play a role in regulating the growth of some galaxies. However, researchers have found other galaxies where the cosmic precipitation has shut off. The intense heat in these central galaxies, possibly from colliding with another galaxy cluster, likely dries up the precipitation around the black hole.

Future studies will be performed to test whether the precipitation-black hole feedback process also regulates star formation in smaller galaxies, including the Milky Way.


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