Hypervelocity stars and the environment of Sgr A*

Hypervelocity stars (HVSs) are a natural consequence of the presence of a massive nuclear black hole (Sgr A*) in the Galactic Centre. Here we use the Brown et al. sample of unbound and bound HVSs together with numerical simulations of the propagation of HVSs in the Milky Way halo to constrain three plausible ejection mechanisms: (i) the scattering of stars bound to Sgr A* by an in-spiralling intermediate-mass black hole (IMBH); (ii) the disruption of stellar binaries in the tidal field of Sgr A*; and (iii) the two-body scattering of stars off a cluster of stellar-mass black holes orbiting Sgr A*. We compare the predicted radial and velocity distributions of HVSs with the limited-statistics data set currently available, and show that the IMBH model appears to produce a spectrum of ejection velocities that is too flat. Future astrometric and deep wide-field surveys of HVSs should shed unambiguous light on the stellar ejection mechanism and probe the Milky Way potential on scales as large as 200 kpc.