Black holes make meals of binary stars

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SALT LAKE CITY, April 2 (UPI) -- U.S. scientists say supermassive black holes in the center of galaxies grow by repeatedly capturing and consuming single stars from pairs that wander too close.

Combining observations of our own Milky Way and other galaxies with new calculations, "we found black holes grow enormously as a result of sucking in captured binary star partners," University of Utah physics and astronomy Professor Ben Bromley said.

"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."

Black holes are more likely to find binary stars within range than single stars, he 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 that hurls a single stone than with a bola that hurls two weights connected by a cord, he explained.

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 said. "The binary doesn't have to get nearly as close for one of the stars to get ripped away and captured."

As many as half of all stars are in binary pairs so they are plentiful in the Milky Way and other galaxies, he said.