A Hypervelocity L Subdwarf Passing Through the Solar Neighborhood

We report the discovery of a very high velocity metal-poor L subdwarf whose kinematics indicate that it is escaping the Milky Way. The source, CWISE J1249+3621, was discovered by citizen scientists as part of the Backyard Worlds: Planet 9 program as a high proper motion (μ = 1.03 arcsec/yr) faint red source. Moderate resolution spectroscopy obtained with Keck/NIRES reveals it to be a metal-poor early L subdwarf with a high radial velocity (-103 km/s). With an estimated distance of 140 pc, CWISE J1249+3621 has a total speed of at least 600 km/s, exceeding the local Galactic escape velocity. Remarkably, the source is moving radially inward, suggesting it was ejected from a globular cluster located in outer Galactic plane in the past 10-30 Myr. CWISE J1249+3621 is the first very low mass star - and the nearest system - found to have an extragalactic trajectory, and may represent a broader population of high-velocity, low-mass ejections from dense cluster systems.