Impact of the Galactic Disk and Large Magellanic Cloud on the Trajectories of Hypervelocity Stars Ejected from the Galactic Center

Abstract

We consider how the gravity of the Galactic disk and the Large Magellanic Cloud (LMC) modifies the radial motions of hypervelocity stars (HVSs) ejected from the Galactic center (GC). For typical HVSs ejected toward low (high) Galactic latitudes, the disk bends trajectories by up to 30° (3°–10°). For many lines of sight through the Galaxy, the LMC produces similar and sometimes larger deflections. Bound HVSs suffer larger deflections than unbound HVSs. Gravitational focusing by the LMC also generates an overdensity of a factor of two along the line of sight toward the LMC. With large enough samples, observations can detect the non-radial orbits and the overdensity of HVSs toward the LMC. For any Galactic potential model, the tangential velocity in the Galactic rest frame provides an excellent way to detect unbound and nearly bound HVSs within 10 kpc of the Sun. Similarly, the radial velocity in the rest frame isolates unbound HVSs beyond 10–15 kpc from the Sun. Among samples of unbound HVSs, measurements of the radial and tangential velocities serve to distinguish GC ejections from other types of high-velocity stars.