Ejection of hypervelocity binary stars by a black hole of intermediate mass orbiting Sgr A

Abstract

The discovery of hypervelocity binary stars (HVBs) in the Galactic halo would provide definite evidence of the existence of a massive black hole companion to Sgr A*. Here, we use a hybrid approach to compute the rate of ejection and the total number of HVBs produced by a hypothetical intermediate-mass black hole (IMBH, M2 < 105 M⊙) orbiting Sgr A*. Depending on the mass of M2 and on the properties of binary stars in the central parsec of the Milky Way, we show that the number of undisrupted HVBs expected to be expelled from the Galactic Centre before binary black hole coalescence ranges from zero to a few dozen at most. Therefore, the non-detection of stellar binaries in a complete survey of hypervelocity stars would not rule out the occurrence of an IMBH-Sgr A* in-spiralling event within the last few × 108 yr. © 2008 The Authors. Journal compilation © 2008 RAS.