Odd behavior of star reveals lonely black hole hiding in giant star cluster

Globular star clusters are huge spheres of tens of thousands of stars that orbit most galaxies. They are among the oldest known stellar systems in the Universe and date back to near the beginning of galaxy growth and evolution. More than 150 are currently known to belong to the Milky Way.

One particular cluster, called NGC 3201and situated in the southern constellation of Vela (The Sails), has now been studied using the MUSE instrument on ESO's Very Large Telescope in Chile. An international team of astronomers has found that one of the stars in NGC 3201 is behaving very oddly—it is being flung backwards and forwards at speeds of several hundred thousand kilometres per hour, with the pattern repeating every 167 days.

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Credit: ESO/L. Calçada

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.

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This important discovery impacts on our understanding of the formation of these star clusters, black holes, and the origins of gravitational wave events.

This short ESOcast takes a look at this discovery and its significance.