The Andromeda Galaxy (M31) is the most distant object in the night sky that can be see with the naked eye, as well as the nearest spiral galaxy to our own Milky Way. Now, scientists using NASA’s Chandra X-ray space telescope over a 13 year period, have announced the discovery of 26 black hole candidates within the galaxy which, combined with previous observations, brings the total number of possible black holes in Andromeda to 35.
Eight of these potential black holes are located within a spherical collection of stars orbiting the galactic core, known as a globular cluster. This bulge of stars in the middle of Andromeda makes it more likely for greater number of black holes to form, and as Stephen Murray of Johns Hopkins University, explains:
“When it comes to finding black holes in the central region of a galaxy, it is indeed the case where bigger is better. In the case of Andromeda we have a bigger bulge and a bigger supermassive black hole than in the Milky Way, so we expect more smaller black holes are made there as well.”
Astrophysicists often experience difficulty distinguishing distant black holes from neutron stars, but in the Andromeda Galaxy these black holes were more easily identified as most have companion stars, whose materials subsequently emit x-rays as it is sucked into the black hole.
This has also lead scientists, including Robin Barnard of the Harvard-Smithsonian Centre for Astrophysics, to believe that the number of black holes so far discovered in Andromeda is just the “tip of the iceberg” and as he explains; “Most black holes won’t have close companions and will be invisible to us.”