Fast-moving stars around an intermediate-mass black hole in ω Centauri.

Black holes have been found over a wide range of masses, from stellar remnants with masses of 5-150 solar masses (M ☉ ), to those found at the centres of galaxies with M > 10 5 M ☉ . However, only a few debated candidate black holes exist between 150M ☉ and 10 5 M ☉ . Determining the population of these intermediate-mass black holes is an important step towards understanding supermassive black hole formation in the early universe 1,2 . Several studies have claimed the detection of a central black hole in ω Centauri, the most massive globular cluster of the Milky Way 3-5 . However, these studies have been questioned because of the possible mass contribution of stellar mass black holes, their sensitivity to the cluster centre and the lack of fast-moving stars above the escape velocity 6-9 . Here we report the observations of seven fast-moving stars in the central 3 arcsec (0.08 pc) of ω Centauri. The velocities of the fast-moving stars are significantly higher than the expected central escape velocity of the star cluster, so their presence can be explained only by being bound to a massive black hole. From the velocities alone, we can infer a firm lower limit of the black hole mass of about 8,200M ☉ , making this a good case for an intermediate-mass black hole in the local universe.