  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.
