  Hills (1988) predicted that runaway stars could be accelerated to velocities
larger than 1000 km/s by dynamical encounters with the supermassive black hole
(SMBH) in the Galactic center. The recently discovered hypervelocity star SDSS
J090745.0+024507 (hereafter HVS) is escaping the Galaxy at high speed and could
be the first object in this class. With the measured radial velocity and the
estimated distance to the HVS, we trace back its trajectory in the Galactic
potential. Assuming it was ejected from the center, we find that a $\sim$ 2
mas/yr proper motion is necessary for the star to have come within a few
parsecs of the SMBH. We perform three-body scattering experiments to constrain
the progenitor encounter which accelerated the HVS. As proposed by Yu &
Tremaine (2003), we consider the tidal disruption of binary systems by the SMBH
and the encounter between a star and a binary black hole, as well as an
alternative scenario involving intermediate mass black holes. We find that the
tidal disruption of a stellar binary ejects stars with a larger velocity
compared to the encounter between a single star and a binary black hole, but
has a somewhat smaller ejection rate due to the greater availability of single
stars.
