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.
@article{arxiv.1805.04184,
title = {Gaia and the Galactic Center Origin of Hypervelocity Stars},
author = {Warren R. Brown and Mario G. Lattanzi and Scott J. Kenyon and Margaret J. Geller},
journal= {arXiv preprint arXiv:1805.04184},
year = {2018}
}