NASA's Chandra finds 'bonanza' of black holes in galaxy next door

Data from NASA's Chandra X-ray Observatory have helped astronomers to discover an unprecedented bonanza of black holes in the Andromeda Galaxy, one of the nearest galaxies to the Milky Way.

Using more than 150 Chandra observations spread over 13 years, researchers identified 26 black hole candidates, the largest number to date, in a galaxy outside our own.

Many consider Andromeda to be a sister galaxy to the Milky Way. The two ultimately will collide, several billion years from now.

“While we are excited to find so many black holes in Andromeda, we think it`s just the tip of the iceberg,” said Robin Barnard of Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., and lead author of a new paper describing these results.

“Most black holes won`t have close companions and will be invisible to us,” he noted.

The black hole candidates belong to the stellar mass category, meaning they formed in the death throes of very massive stars and typically have masses five to 10 times that of our sun.

Astronomers can detect these otherwise invisible objects as material is pulled from a companion star and heated up to produce radiation before it disappears into the black hole.

The research group previously identified nine black hole candidates within the region covered by the Chandra data, and the present results increase the total to 35.

Eight of these are associated with globular clusters, the ancient concentrations of stars distributed in a spherical pattern about the center of the galaxy. This also differentiates Andromeda from the Milky Way as astronomers have yet to find a similar black hole in one of the Milky Way's globular clusters.

Seven of these black hole candidates are within 1,000 light-years of the Andromeda Galaxy's center. That is more than the number of black hole candidates with similar properties located near the center of our own galaxy.

This is not a surprise to astronomers because the bulge of stars in the middle of Andromeda is bigger, allowing more black holes to form.

These results will be published in the June 20 issue of The Astrophysical Journal.