Thousands of stars sparkle in the globular cluster Messier 22 in this image from an amateur astronomer. The cluster contains hundreds of thousands of stars in all. Recent research has revealed that the cluster's core also contains at least two black holes, each of which is 10-20 times the mass of the Sun. Most clusters contain only one black hole, so the presence of two suggests that there could be even more. M22 is in Sagittarius, above the "lid" of the teapot outlined by some of the constellation's brightest stars. [hewholooks/wikimedia]