November 6, 2013
Another Black Hole Found In Globular Cluster
“Astronomers have discover a new black hole candidate sitting inside a globular cluster known as M62. The latest discovery, reported in the Astrophysical Journal, adds weight to the argument that black holes are a common occurrence in these star clusters. Astronomers discovered two black holes in a globular cluster last year known as M22.
"This implies that the discovery of the other black hole, in the globular cluster called M22, was not just a fluke,” said Laura Chomiuk, team member and Michigan State University assistant professor of physics and astronomy. “Black holes really may be common in globular clusters.”
Black holes are stars that have collapsed into themselves and have grown such a strong gravitational field that not even light escapes from them. For a while astronomers assumed that black holes did not occur in globular clusters, which are collections of stars packed together a million times more closely than stars in our galactic neighborhood.
There are so many stars in a globular collection that they often interact with one another. Scientists believe that massive black holes inside a globular cluster would cause violent encounters, making the stars “sling-shot” each other out of the cluster.
Chomiuk said that last year’s discovery of a pair of black holes in a globular cluster was especially surprising because it had been thought that if two black holes dwelled at the center, they would regularly encounter one another until one shoved the other out.
"I think it's safe to say that we have discovered a whole new hunting ground for black holes," Chomiuk said.
The latest black hole, M62-VLA1, was found in a globular cluster located in the constellation Ophiuchus about 22,000 light-years away from Earth. The researchers said that they discovered M62-VLA1 in the core of the cluster using a deep radio continuum imaging from the Karl G. Jansky Very Large Array telescope.
M62-VLA1 is still considered to be a “candidate” for a black hole. The astronomers cautioned in the journal that there are other objects to rule out before defining it as a black hole.
“We cannot yet rule out alternative scenarios for the radio source, such as a flaring neutron star or background galaxy,” the researchers wrote. “Future observations are necessary to determine whether M62-VLA1 is indeed an accreting stellar-mass black hole.”