Old, Metal Poor, Extreme Velocity Stars in Gaia

Within three days of the Gaia DR2 data release Kohei Hattori discovered a population of extreme velocity stars – which at first sight appeared to be above previous estimates of the escape velocity (red dots). But these stars are unlike any other “hyper velocity stars” they are old and metal poor and much more like regular old halo stars. We looked into various ways to accelerate such a significant population of stars, and concluded that despite their high velocities, these stars must actually be bound to the Milky Way. This implies a total Milky Way mass about twice as large as previous estimates. Soon after two other papers used different Gaia tracers to come to the same conclusion. Our paper is here: http://adsabs.harvard.edu/abs/2018ApJ…866..121H