Gaia and the Galactic Center Origin of Hypervelocity Stars

TL;DR

This study uses Gaia data to trace the origins of hypervelocity stars, confirming many originate from the Galactic center and highlighting the potential for future measurements to understand black hole ejections and dark matter distribution.

Contribution

It provides new evidence linking hypervelocity stars to the Galactic center using Gaia data and discusses future prospects for understanding galactic dynamics.

Findings

Halo stars dominate at ~100 km/s below escape velocity

Disk runaways mostly remain bound despite high speeds

Stars ~100 km/s above escape velocity originate from the Galactic center

Abstract

We use new Gaia measurements to explore the origin of the highest velocity stars in the Hypervelocity Star Survey. The measurements reveal a clear pattern in the B-type stars. Halo stars dominate the sample at speeds about 100 km/s below Galactic escape velocity. Disk runaway stars have speeds up to 100 km/s above Galactic escape velocity, but most disk runaways are bound. Stars with speeds about 100 km/s above Galactic escape velocity originate from the Galactic center. Two bound stars may also originate from the Galactic center. Future Gaia measurements will enable a large, clean sample of Galactic center ejections for measuring the massive black hole ejection rate of hypervelocity stars, and for constraining the mass distribution of the Milky Way dark matter halo.