SIMBAD references

Hypervelocity stars (HVSs) found in the Galactic halo are believed to be the dynamical products of interactions between (binary) stars and the massive black hole(s) (MBH) in the Galactic center (GC). In this paper, we investigate how the spatial and velocity distributions of HVSs are connected with their originations, ejecting mechanisms, and the dynamical environment in the GC. It has been shown that the detected HVSs are spatially consistent with being located on two thin disks (Lu et al.), one of which has the same orientation as the clockwise rotating stellar disk in the GC. Here, we perform a large number of three-body experiments of the interactions between the MBH and binary stars bound to it; and we find that the probability of ejecting HVSs is substantially enhanced by multiple encounters between the MBH and binary stars at a distance substantially larger than their initial tidal breakup radii. Assuming that the HVS progenitors are originated from the two thin disks, our simulations show that the distributions of the HVS inclination relative to the disk planes can be well reproduced by either the mechanism of tidal breakup of binary stars or the mechanism of ejecting HVSs by a hypothetical binary black hole (BBH) in the GC. However, an isotropical origination of HVS progenitors is inconsistent with the observed inclination distribution. Assuming that the detected HVSs were ejected out by tidal breakup of binary stars, its velocity distribution can be reproduced if their progenitors diffuse onto low angular momentum orbits slowly and most of the progenitors were broken up at relatively large distances because of multiple encounters. Assuming that the HVSs were ejected out by a BBH within the allowed parameter space in the GC, our simulations produce relatively flatter spectra at the high-velocity end compared with the observed ones; however, the BBH mechanism cannot be statistically ruled out, yet. Future deep surveys of HVSs and better statistics of the HVS spatial and velocity distributions should enable the ejection mechanisms of HVSs to be distinguished and shed new light on the dynamical environment surrounding the central MBH.