Black Hole Bonanza Observed in Andromeda Galaxy, NASA Says

NASA astronomers observed more than two dozen potential black holes in the nearby Andromeda Galaxy, a discovery the space agency called "unprecedented."

Twenty-six potential black holes were identified, the largest number ever discovered in a galaxy outside of our own Milky Way. The black hole bonanza was observed with data from the Chandra X-Ray Observatory, which made more than 150 observations over the past 13 years.  

Robin Barnard of Harvard-Smithsonian Center for Astrophysics (CfA) and lead author or the study on Andromeda's black holes, said he was excited about the discovery but that it was just the tip of the iceberg.   

The potential black holes are believed to have formed as stars up to 10 times the mass of our Sun were dying.

When coupled with the nine other black hole candidates already identified within the region of Andromeda the Chandra data covered, the total of black hold candidates observed rises to 35.

Eight of these are associated with globular clusters, the ancient concentrations of stars distributed around the center of the galaxy, and seven of the candidates are within 1,000 light-years of the Andromeda Galaxy's center, which NASA says is more than the number of black hole candidates with similar properties located near the center of our own galaxy. 

However, astronomers were not surprised to find more black holes in Andromeda; its center has a lot more stars than our own, allowing for more black holes.

"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," Stephen Murray of the CfA said in a NASA statement.

"It is indeed the case where bigger is better," he said

While the black holes cannot be observed directly, astronomers can detect the presence of them by observing what happens as material is pulled from a companion star and heated up to produce radiation before it disappears into the black hole.

"We are particularly 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," said Barnard. 

Andromeda, also known as Messier 31 (M31), is a spiral galaxy located about 2.5 million light years away. It is thought that the Milky Way and Andromeda will collide several billion years from now. The black holes located in both galaxies will then reside in the large, elliptical galaxy that results from this merger, according to NASA.