Galactic 'Rain' Answers Why Some Galaxies are Better at Birthing Stars Than Others

While some galaxies are veritable star nurseries, others went barren years ago. Yet what causes some galaxies to produce new stars while others go silent? That's a good question and now, astronomers may have found the answer.

The researchers believe that it could be due to galactic "rain." Obviously, this isn't in the form of rain or snow, but rather in the form of cool gas that helps make the creation of stars possible.

"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 create stars. However, some of these clouds of gas fall into the massive black holes that reside in the center of galaxy clusters. This, in turn, triggers the production of jets that reheat the gas and then prevent more stars from forming.

In order to better understand this phenomenon, the researchers studied more than 200 galaxy clusters. They found that the process of precipitation affected the environment around some of the largest black holes. The galaxies within these clusters that were surrounded by enormous atmospheres of hot gas that normally would cool to form many stars actually had only feeble amounts of stars forming.

"Something is limiting the rate at which galaxies can turn that gas into stars and planets," said Voit. "I think we're finally getting a handle on how this all works."

The 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.

The findings are published in the journal Nature.

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