Some galaxies, like the Milky Way, are veritable star nurseries, giving birth to at least one baby star every year. Others are barren. Until now, astronomers haven’t been sure why.
A new study shows that a galaxy’s fertility may depend on galactic “rain.”
“We know that precipitation can slow us down on our way to work,” says 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.”
Like a blowtorch
Obviously it’s 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.
But, some of the clouds fall into the massive black holes that reside at the center of the galaxy clusters. That triggers the production of jets that reheat the gas like a blowtorch, preventing more stars from forming.
For the study, published in the journal Nature, researchers used NASA’s Chandra X-ray Observatory to analyze X-rays from more than 200 galaxy clusters and pinpoint how precipitation affects the environment around some of the universe’s largest black holes.
All dried up
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.
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.
Other researchers from Michigan State, and from Massachusetts Institute of Technology and from Columbia University contributed to the study.
Source: Michigan State University