The star grinder in the Galactic centre

Abstract

Context. Various past theoretical considerations and observational efforts suggest the presence of a population of stellar-mass black holes in the innermost parsec of the Galactic centre.Aims. In this Letter, we investigate the impact of these black holes on the composition of the embedding stellar population through their direct collisions with the individual stars. Based on the estimated collision rates, we derive an order of magnitude radial density profile of the black hole cluster.Methods. The estimates were obtained analytically, considering various possible formation channels for the black holes and the observed present-day properties of the stellar populations in the Galactic centre.Results. We find that the collisions of the stars and the black holes can lead to the depletion of the most massive stars within the S-cluster on a timescale of a few million years. The necessary black hole cluster density is compatible with the recurrent in situ star formation in the innermost parsec of the Galactic centre. We suggest that such a depletion naturally explains the reported lack of stars of the stellar type O and of the Galactic halo hyper-velocity star counterparts within the S-cluster.