2008MNRAS.383...86O

Stars within 0.1pc of the supermassive black hole (BH) SgrA* at the Galactic Centre are expected to encounter a cluster of stellar-mass BHs that have segregated to that region. Some of these stars will scatter off an orbiting BH and be kicked out of the Galactic Centre with velocities up to ∼2000km/s. We calculate the resulting ejection rate of hypervelocity stars (HVSs) by this process under a variety of assumptions, and find it to be comparable to the tidal disruption rate of binary stars by SgrA*, first discussed by Hills. Under some conditions, this novel process is sufficient to account for all of the hypervelocity B stars observed in the halo, and may dominate the production rate of all HVSs with lifetimes much less than the relaxation time-scale at a distance ∼2pc from SgrA* (≳2Gyr). Since HVSs are produced by at least two unavoidable processes, the statistics of HVSs could reveal bimodal velocity and mass distributions, and can constrain the distribution of BHs and stars in the innermost 0.1pc around SgrA*.