Black holes 'eat binary star partners' to grow
Washington: Researchers have come up with a new explanation for the growth of supermassive black holes in the centre of most galaxies asserting that they constantly capture and swallow single stars from pairs of stars that wander too close.
Using new calculations and previous observations of our own Milky Way and other galaxies, “we found black holes grow enormously as a result of sucking in captured binary star partners,” said physics and astronomy Professor Ben Bromley, lead author of the study.
“I believe this has got to be the dominant method for growing supermassive black holes,” he said.
“There are two ways to grow a supermassive black hole: with gas clouds and with stars. Sometimes there’s gas and sometimes there is not. We know that from observations of other galaxies. But there are always stars.”
“Our mechanism is an efficient way to bring a star to a black hole,” Bromley said.
“It’s really hard to target a single star at a black hole. It’s a lot easier to throw a binary at it,” just as it’s more difficult to hit a target using a slingshot, which hurls a single stone, than with a bola, which hurls two weights connected by a cord.
A binary pair of stars orbiting each other “is essentially a single object much bigger than the size of the individual stars, so it is going to interact with the black hole more efficiently,” he explained.
“The binary doesn’t have to get nearly as close for one of the stars to get ripped away and captured.”
But to prove the theory will require more powerful telescopes to find three key signs: large numbers of small stars captured near supermassive black holes, more observations of stars being “shredded” by gravity from black holes, and large numbers of “hypervelocity stars” that are flung from galaxies at more than 1 million mph when their binary partners are captured.
Bromley, a University of Utah astrophysicist, refers to the process of a supermassive black hole capturing stars from binary pairs as “filling the bathtub.”
Once the tub – the area near the black hole – is occupied by a cluster of captured stars, they go “down the drain” into the black hole over millions of years.
His study shows the “tub” fills at about the same rate it drains, meaning stars captured by a supermassive black hole eventually are swallowed.
The study has been recently published in Astrophysical Journal Letters.