  Young stars observed in the distant Galactic halo are usually thought to have
formed elsewhere, either in the Galactic disk or perhaps the Galactic center,
and subsequently ejected at high velocities to their current position. However,
some of these stars have apparent lifetimes shorter the required flight time
from the Galactic disk/center. We suggest that such stars have evolved in close
runaway or hypervelocity binaries. Stellar evolution of such binaries can drive
them into mass transfer configurations and even mergers. Such evolution could
then rejuvenate them (e.g. blue stragglers) and extend their lifetime after
their ejection. The extended lifetimes of such stars could then be reconciled
with their flight times to the Galactic halo. We study the possibilities of
binary runaway and hypervelocity stars and show that such binaries could have
been ejected in triple disruptions and other dynamical interactions with stars
or with massive black holes. We show that currently observed "too young" star
in the halo could have been ejected from the Galactic disk or the Galactic
center and be observable in their current position if they were ejected as
binaries. Specifically it is shown that the hypervelocity star HE 0437-5439
could be such a rejuvenated star. Other suggestions for its ejection from the
LMC are found to be highly unlikely. Moreover, it is shown that its observed
metallicity is most consistent with a Galactic origin and a Galactic center
origin can not currently rule out. In addition, we suggest that triple
disruptions by the massive black hole in the Galactic center could also capture
binaries in close orbits near the MBH, some of which may later evolve to become
more massive rejuvenated stars.

Astrophysics