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Black Holes Grow Fat by Eating Stars

By David Reneke

News from the space and astronomy communities around the world.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at

The full text of this article can be purchased from Informit.

Black holes are objects in space so dense that not even light can escape their gravity, although powerful jets of light and energy can be emitted from a black hole’s vicinity as gas and stars are sucked into it.

Small black holes result from the collapse of individual stars, but the centres of most galaxies – including our own Milky Way – are occupied by supermassive black holes with masses between one million and ten billion times that of our Sun.

New research being carried out at the University of Utah and the Harvard-Smithsonian Centre for Astrophysics (CfA) shows that supermassive black holes can grow bigger by ripping apart double star systems and swallowing one of the stars. Tidal forces capture one star and eject the other. The captured star orbits around the black hole, later becoming fodder for the galactic monster.

“Black holes are very efficient eating machines,” said Scott Kenyon of the CfA. “They can double their mass in less than a billion years. That may seem long by human standards, but over the history of the galaxy it’s pretty fast.”

As many as half of all stars are in binary pairs. Crunching the numbers, the rate of observed binary encounters with our galaxy’s supermassive black hole would mean that most of the mass of the black hole came from binary stars. The same seems to apply in other galaxies as well.


The full text of this article can be purchased from Informit.