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 (μα,μδ) = (+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 3σ 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.