  Halo stars with unusually high radial velocity ("hypervelocity" stars, or
HVS) are thought to be stars unbound to the Milky Way that originate from the
gravitational interaction of stellar systems with the supermassive black hole
at the Galactic center. We examine the latest HVS compilation and find
peculiarities that are unexpected in this black hole-ejection scenario. For
example, a large fraction of HVS cluster around the constellation of Leo and
share a common travel time of $\sim 100$-200 Myr. Furthermore, their velocities
are not really extreme if, as suggested by recent galaxy formation models, the
Milky Way is embedded within a $2.5\times 10^{12} h^{-1} M_{\odot}$ dark halo
with virial velocity of $\sim 220$ km/s. In this case, the escape velocity at
$\sim 50$ kpc would be $\sim 600$ km/s and very few HVS would be truly unbound.
We use numerical simulations to show that disrupting dwarf galaxies may
contribute halo stars with velocities up to and sometimes exceeding the nominal
escape speed of the system. These stars are arranged in a thinly-collimated
outgoing ``tidal tail'' stripped from the dwarf during its latest pericentric
passage. We speculate that some HVS may therefore be tidal debris from a dwarf
recently disrupted near the center of the Galaxy. In this interpretation, the
angular clustering of HVS results because from our perspective the tail is seen
nearly ``end on'', whereas the common travel time simply reflects the fact that
these stars were stripped simultaneously from the dwarf during a single
pericentric passage. This proposal is eminently falsifiable, since it makes a
number of predictions that are distinct from the black-hole ejection mechanism
and that should be testable with improved HVS datasets.
