A new study has revealed that cosmic showers or galactic rain can halt star formation in galaxies with huge black holes.
Using NASA's Chandra X-ray Observatory, astronomers have found that the growth of galaxies containing supermassive black holes can be slowed down by a phenomenon referred to as cosmic precipitation.
Cosmic precipitation is not a weather event; as it's commonly associated with the words- rain, sleet, or snow. Rather, it's a mechanism that allows hot gas to produce showers of cool gas clouds that fall into a galaxy. Researchers have analyzed X-rays from more than 200 galaxy clusters, and believe that this gaseous precipitation was key to understanding how giant black holes affect the growth of galaxies.
The study looked 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 was hindering the star birth.
The answer appeared to lie with the supermassive black holes at the centers of the large galaxies. Under specific conditions, clumps of gas can 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, triggering jets of energetic particles that push against the falling gas and reheat it, preventing more stars from forming. This cycle of cooling and heating creates a feedback loop that regulates the growth of the galaxies.
Researchers 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 Chandra data indicated that the regulation of this precipitation has been going on for the last 7 billion years or more.
While a rain of cool clouds appears to play a key role in regulating the growth of some galaxies, the researchers have found other galaxies where the cosmic precipitation had shut off. The intense heat in these central galaxies, possibly from colliding with another galaxy cluster, likely "dried up" the precipitation around the black hole.
The study is published in the journal Nature.
