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

TL;DR

This study examines how the gravitational effects of the Galactic disk and Large Magellanic Cloud influence the trajectories of hypervelocity stars ejected from the Galactic Center, affecting their observed motions and distributions.

Contribution

It provides detailed modeling of how the Galactic disk and LMC alter hypervelocity star trajectories, highlighting observational signatures for identifying their origins.

Findings

Disk and LMC cause significant trajectory deflections.

LMC induces overdensity of HVSs along its line-of-sight.

Velocity measurements help distinguish ejected stars from other high-velocity stars.

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. For typical HVSs ejected towards low (high) Galactic latitudes, the disk bends trajectories by up to 30 degrees (3-10 deg). 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 a factor of two overdensity along the line-of-sight towards the LMC. With large enough samples, observations can detect the non-radial orbits and the overdensity of HVSs towards the LMC. For any Galactic potential model, the Galactic rest-frame tangential velocity provides an excellent way to detect unbound and nearly bound HVSs within 10 kpc of the Sun. Similarly, the rest-frame radial velocity isolates unbound HVSs beyond 10-15 kpc from the Sun. Among samples of unbound HVSs, measurements of the radial and tangential velocity serve to distinguish Galactic Center ejections from other types of high velocity stars.