The central region of the Andromeda galaxy is chock-full of black holes, according to extensive observations with NASA's Chandra X-ray Observatory. 26 new stellar-mass black hole candidates have been identified, adding to nine previously known and bringing the grand total to 35.
It might not sound like a lot compared to the size of an entire galaxy, but it's many more than have been found so far in our own galaxy's center and indicates the presence of even more that can't be seen.
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"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), lead author of a new paper describing these results. "Most black holes won't have close companions and will be invisible to us."
Using data from Chandra and the European Space Agency's XMM-Newton X-ray Observatory, astronomers were able to spot these otherwise invisible objects by the energy released by superheated material they draw in from nearby stars.