2018AJ....156...87L

In this paper, we report the discovery of a new late-B-type unbound hyper-runaway star (LAMOST-HVS4) from the LAMOST spectroscopic surveys. According to its atmospheric parameters, it is either a B-type main-sequence (MS) star or a blue horizontal branch (BHB) star. Its Galactocentric distance and velocity are 30.3 ± 1.6 kpc and 586 ± 7 km s^–1 if it is an MS star, and they are 13.2 ± 3.7 kpc and 590 ± 7 km s^–1 if a BHB star. We track its trajectories back and find that the trajectories intersect with the Galactic disk, and the Galactic center lies outside of the intersection region at the 3σ confidence level. We investigate a number of mechanisms that could be responsible for the ejection of the star and find that it is probably ejected from the Galactic disk by supernova explosion or multiple-body interactions in dense young stellar clusters.