Black Holes Block New Stars From Forming

Big black holes spew out "radio frequency feedback" that, traveling at near-light speed, can block new stars from forming in aging galaxies, according to a new study.

"When you look into the past history of the Universe, you see these galaxies building stars," Tobias Marriage from Johns Hopkins University, the study's co-author, said in a statement. "At some point, they stop forming stars and the question is: Why? Basically, these active black holes give a reason for why stars stop forming in the Universe."

Stars form when hot free gas drawn into a galaxy cools and condenses. Some gas also funnels down into the galaxy's black hole, which grows and grows while baby stars form. Given this continuous cycle, at some point the galaxy's central black hole gets so massive that the gas doesn't cool any more.

"If gas is kept hot, it can't collapse," Marriage said. So in these mature galaxies - big galaxies called "elliptical" because of their shape - no new stars form.

Using a well-known technique called the Sunyaev-Zel'dovich effect signature - typically used to study large galaxy clusters - researchers realized that the elliptical galaxies were shooting out radio-frequency-emitting particles from their black holes at nearly the speed of light. What's more, this feedback contained hot gas and lacked infant stars, providing evidence that this feature was the "off switch" for star-making in mature galaxies.

"What we're doing is asking a different question than what has been previously asked," added postdoctoral fellow Megan Gralla. "We're using a technique that's been around for some time and that researchers have been very successful with, and we're using it to answer a totally different question in a totally different subfield of astronomy."

Researchers still aren't sure what exactly causes black holes to emit star-killing, radio-frequency feedback, but the new study poses "new challenges to the theory of galaxy formation, as there were hardly any data which told us how much hot gas there is around galaxies," according to astrophysics expert Eiichiro Komatsu, who was not involved in the study.

The findings were published in the journal Monthly Notices of the Royal Astronomical Society.