Some of the galaxies in our universe are veritable star nurseries. For example, our own Milky Way produces, on average, at least one new star every year. Others went barren years ago, now producing few if any new stars. Why that happens is a question that has dogged astronomers for years.
But now, using Chandra, which, at an altitude of 139,000 kilometers (86,500 miles) can observe galaxies and stars free from any distortion caused by Earth’s atmosphere, researchers examined X-rays from over 200 galaxy clusters. They postulate that gaseous precipitation is crucial to understanding the influence of giant black holes on the growth of galaxies.
“We know that precipitation can slow us down on our way to work,” said Mark Voit, one of the researchers, in a news release. “Now we know it can also slow down star formation in galaxies with huge black holes.”
When conditions are right, cooling gas clouds help make stars. However, some of the clouds fall into the massive black holes that reside at the centre of the galaxy clusters. That triggers the production of jets that reheat the gas like a blowtorch, preventing more stars from forming.
The researchers could pinpoint how this process of precipitation affects the environment around some of the universe’s largest black holes.
The galaxies within these clusters are surrounded by enormous atmospheres of hot gas that normally would cool and form many stars. However, this is not what astronomers see. Usually there are only feeble amounts of stars forming.
“Something is limiting the rate at which galaxies can turn that gas into stars and planets,” Voit says. “I think we’re finally getting a handle on how this all works.”
While precipitation plays a key role in some galaxies, there are others in which the precipitation has shut off. In these galaxies, the movement of heat around the central galaxy, perhaps due to a collision with another galaxy cluster, likely “dried up” the precipitation around the black hole.
This findings reveal a bit more about star formation in these galaxies. More specifically, it shows how the interaction between gas, dark holes and this “precipitation” can limit or help star formation.
Bottom line: A galaxy cluster can contain anywhere from 50 to 1,000 galaxies. The Milky Way is part of a cluster known as the Local Group, which contains about 50.