Winds Blasting From Black Holes Shut Down Star Growth
Astronomers catch hot gases streaming from a distant quasar and disrupting clouds where new stars form.
A black hole in a distant galaxy pumps out winds traveling at a blistering one-third the speed of light, giving astronomers the best evidence yet that black holes can both limit their own growth and shut down star formation in their neighborhoods.
The evidence, reported Thursday in Science, comes in the form of X-rays streaming from a quasar—a spot of light so bright that it outshines an entire galaxy—located just over two billion light-years from Earth. "It's a very nice observation," says Princeton astrophysicist Jenny Greene, who was not involved with the research.
In fact, a quasar is a black hole. More precisely, it's an accretion disk, a pancake-shaped cloud of gas that heats up to millions of degrees as it tries to cram its way down into the voracious gravitational field of a giant black hole. (Learn how black holes work in "Star Eater.")
Virtually every galaxy, including our own Milky Way, harbors a supermassive black hole in (or near) its core, weighing as much as millions, or even billions, of stars.
Not every supermassive black hole lights up a quasar, however, and the new observations help demonstrate why. Using both the XMM-Newton and NuSTAR space telescopes, lead author Emanuele Nardini of Keele University in the U.K. and colleagues mapped out a "wind" of hot gas streaming away from the quasar known as PDS 456, located in the constellation Serpens.
"We've seen gas coming toward us from a quasar before," says Nardini, "but this is the first time we can show that it's moving out in all directions."
Winds of Destruction
The outward-streaming gas is powered by intense light coming out of the accretion disk, Nardini says. As the gas is swept away, the accretion disk, and ultimately the black hole itself, becomes starved for new material.
"The wind," Nardini says, "is regulating the growth of the black hole."
The wind then goes on to stunt the growth of nearby stars. As the expanding bubble of gas moves farther out, it pushes apart the giant molecular clouds where new stars form.
The self-starving, star-quenching bubble of hot gas that Nardini and his colleagues see in PDS 456 is probably typical of what's happening in most quasars, they think. The big difference is that most other quasars are much farther away from Earth, which means the light we see from them was emitted when the universe—and the supermassive black holes inside galaxies—were much younger than they are now.
Plenty of nearby galaxies, in other words, went through a quasar phase in their youth but, thanks to the process described in the new observations, have settled down into a much quieter middle age. It just happens that PDS 456 is a late bloomer.
In fact, you can think of this quasar as a living fossil—ancient in its appearance, but youthful enough that astronomers can study it in detail. "It's one of a kind," says Nardini.
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