Surprising black hole discovery changes picture of globular star clusters
An unexpected discovery is forcing scientists to rethink their understanding of the environment in globular star clusters, tight-knit collections containing hundreds of thousands of stars. The astronomers were studying a globular cluster called Messier 22 (M22), a group of stars more than 10,000 light-years from Earth. They hoped to find evidence of a rare type of black hole in the cluster's center called an intermediate-mass black hole, which is more massive than those larger than the Sun's mass, but smaller than the supermassive black holes found at the cores of galaxies. However, they found something very surprising - two smaller black holes, which is unusual because most theorists say there should be at most one black hole in the cluster.