A Galactic Center Origin for HE 0437-5439, the Hypervelocity Star near the Large Magellanic Cloud

Abstract

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 (μ_α, μ_δ)=(+0.53+-0.25(stat)+-0.33(sys), +0.09+-0.21(stat)+-0.48(sys)) mas/yr. 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.

5 pages, accepted in ApJ Letters

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• The fate of close encounters between binary stars and binary supermassive black holes
• Hypervelocity star candidates from Gaia DR2 and DR3 proper motions and parallaxes
• Binary Natal Kicks in the Galactic Center: X-ray Binaries, Hypervelocity Stars, and Gravitational Waves
• Searching for new Hypervelocity Stars with Gaia DR3 and VLT/FORS2 Spectroscopy
• On Stellar Migration from Andromeda to the Milky Way
• Local Group Proper Motion Dynamics
• The chemical and spatial variations of the bulge's velocity ellipsoids