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 > 10⁵M_☉. However, only a few debated candidate black holes exist between 150M_☉ and 10⁵M_☉. 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.