A GALACTIC ORIGIN FOR HE 0437-5439, THE HYPERVELOCITY STAR NEAR THE LARGE MAGELLANIC CLOUD

We use Hubble Space Telescope imaging to measure the absolute proper motion of the hypervelocity star (HVS) HE 0437-5439, a short-lived B star located in the direction of the Large Magellanic Cloud (LMC). We observe (mu(alpha), mu(delta)) = (+0.53 +/- 0.25(stat) +/- 0.33(sys), + 0.09 +/- 0.21(stat) +/- 0.48(sys)) mas yr(-1). The velocity vector points directly away from the center of the Milky Way; an origin from the center of the LMC is ruled out at the 3 sigma level. The flight time of the HVS from the Milky Way exceeds its main-sequence lifetime, thus its stellar nature requires it to be a blue straggler. The large space velocity rules out a Galactic-disk ejection. Combining the HVS's observed trajectory, stellar nature, and required initial velocity, we conclude that HE 0437-5439 was most likely a compact binary ejected by the Milky Way's central black hole.