Hypervelocity star LAMOST-HVS1 was ejected from the Milky Way disk!

LAMOST HVS1 is a hypervelocity star which was originally thought to have been ejected from the Galactic Center by an interaction with the supermassive black hole. However, Gaia data for its proper motion indicates that it was ejected from the disk. The blue dots in the top panel show where this object was probably ejected from. The colored curves mark the locations of various spiral arms. It looks like this star was ejected with a velocity of > 560km/s from a massive star cluster in the Norma Spiral arm (purple curve) about 38Million years ago. This has important implications for other claimed Hypervelocity stars – which could be ejected from multiple-star interactions in clusters rather than by massive black holes! The paper is here: http://adsabs.harvard.edu/abs/2018arXiv181002029H