Astronomers have discovered the largest ever collection of black holes outside of our own galaxy.
Andromeda, our closest neighboring galaxy, has a larger supermassive black hole at its center than ours, and also has a larger "bulge" of center stars than us. That was the first clue that the galaxy likely has many black holes.
Researchers found a total of 26 potential black holes, plus the additional nine already known in the Andromeda galaxy. The total now stands at 35.
These black holes are not as large as the supermassive ones at the centers of many galaxies, as they are only about five to 10 times more massive than our sun. Black holes are formed when giant stars die, and have such strong gravitational pulls that they suck anything nearby into it, including light.
Robin Barnard, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said, "While we are excited to find so many black holes in Andromeda, we think it's just the tip of the iceberg. Most black holes won't have close companions and will be invisible to us."
"We are partially excited to see so many black hole candidates this close to the center, because we expected to see them and have been searching for years."
"When it comes to finding black holes in the central region of a galaxy, it is indeed the case where bigger is better," co-author Stephen Murray of Johns Hopkins University said. "In the case of Andromeda, we have a bigger bulge and a bigger super massive black hole than in the Milky Way, so we expect more smaller black holes are made there as well."
Scientists found the black holes using NASA's Chandra X-Ray Observatory. It took them 13 years to make the discoveries. They observe X-ray light given off by the objects to differentiate them from other dense objects like neutron stars.