Threading the Magellanic Needle: Hypervelocity Stars Trace the Past Location of the LMC

TL;DR

This study leverages three LMC-origin hypervelocity stars (HVS 3, HVS 7, HVS 15) with ejection times spanning $30$–$400\,\mathrm{Myr}$ ago to constrain the LMC's past orbit around the Milky Way. By back-integrating the HVS trajectories in a time-evolving LMC–MW potential and treating the stars as test particles, the authors derive posterior distributions for the LMC's orbital history conditioned on intersections with the LMC center. They find two previously published orbital models that align with these new constraints: a first-passage trajectory from a hydrodynamic simulation and a second-passage trajectory from a collisionless N-body simulation. The approach also yields an independent inference of the present-day ejection site, likely the LMC’s dynamical center and central black hole, enhancing our understanding of MW–LMC dynamics beyond traditional methods.

Abstract

Recent discoveries have shown that a population of hypervelocity stars (HVSs) originate from the Large Magellanic Cloud (LMC). We use three such HVSs as dynamical tracers to constrain the past orbit of the LMC. Since each star was ejected at a finite time in the past, it must intersect the past position of the LMC's central black hole at its ejection time. We model the LMC's orbit under the influence of dynamical friction and extended mass distributions for both the LMC and the Milky Way, generating a large ensemble of orbital realizations. By evaluating which orbits intersect the back-integrated HVS trajectories, we compute posterior distributions over the LMC's orbital history. This approach provides significantly tighter constraints on the past motion of the LMC than previously possible. We find two previously published orbital models that are consistent with these new constraints: a first-passage trajectory from a self-consistent hydrodynamic simulation, and a second-passage trajectory from a collisionless N-body simulation. In parallel, we infer the present-day ejection site of the HVSs -- likely tracing the LMC's dynamical center and supermassive black hole -- independent of conventional methods.