The former companion of the hyper-velocity star S5-HVS1
  The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Center
at 1800 km/s, was most likely produced by tidal break-up of a tight binary by
the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that
the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and
6 solar masses and was captured into a highly eccentric orbit with pericenter
distance in the range 1-10 AU and semimajor axis about $10^3$ AU. We then
explore the fate of the captured star. We find that the heat deposited by
tidally excited stellar oscillation modes leads to runaway disruption if the
pericenter distance is smaller than about 3 AU. Over the past 5 Myr, its
angular momentum has been significantly modified by orbital relaxation, which
may stochastically drive the pericenter inwards below 3 AU and cause tidal
disruption. We find an overall survival probability in the range 5% to 50%,
depending on the local relaxation time in the close environment of the captured
star, and the initial pericenter at capture. The pericenter distance of the
surviving star has migrated to 10-100 AU, making it potentially the most
extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like
stars, we estimate that there may currently be a few stars in such highly
eccentric orbits. They should be detectable (typically Ks < 18.5 mag) by the
GRAVITY instrument and by future Extremely Large Telescopes and hence provide
an extraordinary probe of the spin of SgrA*.
