spacetoday.net: Black hole pair found in star cluster

Posted: Thu, Oct 4, 2012, 7:45 AM ET (1145 GMT)
Astronomers reported this week the discovery of two black holes in the center of a globular star cluster where only one was expected to exist. Astronomers using the Jansky Very Large Array (VLA) radio telescope in New Mexico reported finding two stellar-mass black holes in the core of the cluster M22. That discovery is in contrast to models of cluster formation, which predict that all but one black holes formed in the cluster would eventually be thrown out through gravitational interactions with each other. Astronomers suggest that the core of the cluster may not be as dense as originally thought, which would slow down the rate at which black holes are ejected.