The spatial and velocity distributions of hypervelocity stars
  Hypervelocity stars (HVSs) found in the Galactic halo are probably the
dynamical products of interactions between (binary) stars and the massive black
hole(s) (MBH) in the Galactic center (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 find that the
probability of ejecting HVSs is substantially enhanced by multiple encounters
between the MBH and binary stars at distances substantially larger than the
initial tidal breakup radii. Assuming that the HVS progenitors are originated
from the two disks, the inclination distribution of the HVSs relative to the
disk planes can be 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 HVSs
were ejected out by the tidal breakup mechanism, 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
due to 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 velocity spectra compared to the observed ones; however, the
BBH mechanism cannot be statistically ruled out, yet. Future surveys of HVSs
and better statistics of their spatial and velocity distributions should enable
to distinguish the ejection mechanisms of HVSs and shed new light on the
dynamical environment of the MBH.(abridged)
