Galactic 'rain' could slow down star formation

Pouring cool gases called galactic "rain" may slow down star formation in certain galaxies, astronomers have found.

"We know that precipitation can slow us down on our way to work," said lead researcher Mark Voit, professor of physics and astronomy at Michigan State University.

"Now we know it can also slow down star formation in galaxies with huge black holes," Voit added.

"Obviously, it is not in the form of rain or snow, but rather cool gas that helps make the creation of stars possible. When conditions are right, these cooling gas clouds help make stars," the researchers said.

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 astronomers explained.

The findings could explain why some galaxies are better than others at creating stars. 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.

The researchers, using NASA's Chandra X-ray Observatory, analysed X-rays from more than 200 galaxy clusters. They could pinpoint how this process of precipitation affects the environment around some of the universe's largest black holes.

The study was published in the journal Nature.