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

TL;DR

This study measures the proper motion of the hypervelocity star HE 0437-5439, concluding it likely originated from the Milky Way's center, not the Large Magellanic Cloud, and is probably a blue straggler ejected by the galactic black hole.

Contribution

The paper provides the first proper motion measurement of HE 0437-5439, ruling out LMC origin and supporting a galactic center ejection scenario.

Findings

Proper motion points away from the Milky Way center

Origin from the LMC is statistically ruled out

Star is likely a blue straggler ejected by the galactic black hole

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 (\mu_\alpha, \mu_\delta)=(+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.