Artist’s impression of the black hole binary system in NGC 3201

Astronomers using ESO’s MUSE instrument on the Very Large Telescope in Chile have discovered a star in the cluster NGC 3201 that is behaving very strangely. It appears to be orbiting an invisible black hole with about four times the mass of the Sun — the first such inactive stellar-mass black hole found in a globular cluster. This important discovery impacts on our understanding of the formation of these star clusters, black holes, and the origins of gravitational wave events.This artist’s impression shows how the star and its massive but invisible black hole companion may look, in the rich heart of the globular star cluster.