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How do supermassive black holes get so big? A peculiar diet, perhaps.

New research suggests that the supermassive black holes at the cores of some galaxies could grow so large by consuming one star from a binary system and flinging the other into space.

An image from data provided by the Chandra X-ray Observatory shows Sagittarius A, the supermassive black hole at the center of the Milky Way Galaxy.


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For years, astronomers have puzzled over the diet needed to bulk up supermassive black holes – powerful gravitational traps that lurk in the centers of galaxies.

Now, scientists have added a new ingredient that they say could account for a substantial portion of a supermassive black hole's heft: stars wrested from binary star systems that wandered too close for their own good.

One star in a binary paring gets ejected from the galaxy at extraordinary speeds. The star left behind orbits even closer to the black hole, joining other stars the black hole has orphaned.

At some point, the zone in which the orphans orbit reaches its capacity. After that, gravitational interactions between all the orphans virtually guarantee that when a new star enters the zone, another star must vanish into the black hole itself, signaling its end with a brief flash of high-energy radiation.

Since about half of the stars in the galaxy appear as binary pairs, they should be abundant enough to feed the process, the team holds.

The calculations that led to this scenario represent “a proof of concept,” notes Scott Kenyon, a researcher at the Harvard-Smithsonian Center for Astrophysics, based in Cambridge, Mass., and a member of the team formally presenting the scenario today in the journal Astrophysical Journal Letters

Processes operating at the heart of the Milky Way, and by extension other galaxies, aren't well understood, Dr. Kenyon explains. The team hopes its work will help open a window on those processes – in particular, how supermassive black holes grow.

Black holes are objects with gravity so strong that not even light can escape. So-called stellar mass black holes form from the remnants of a massive star that ends its life in an enormous explosion known as a supernova.


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