A high-velocity star recently ejected by an intermediate-mass black hole in M15

TL;DR

This paper reports the discovery of a high-velocity star ejected from globular cluster M15, providing strong evidence for the presence of an intermediate-mass black hole at its center.

Contribution

It presents observational evidence linking a high-velocity star to an IMBH in M15, supporting the existence of such black holes in globular clusters.

Findings

High-velocity star likely ejected from M15's center

Star's properties match those of M15

Evidence confirms IMBH in M15 with >98% credibility

Abstract

The existence of intermediate-mass black holes (IMBHs) is crucial for understanding various astrophysical phenomena, yet their existence remains elusive, except for the LIGO-Virgo detection. We report the discovery of a high-velocity star J0731+3717, whose backward trajectory about 21 Myr ago intersects that of globular cluster M15 within the cluster tidal radius. Both its metallicity [Fe/H] and its alpha-to-iron abundance ratio [$\alpha$/Fe] are consistent with those of M15. Furthermore, its location falls right on the fiducial sequence of the cluster M15 on the color-absolute magnitude diagram, suggesting similar ages. These support that J0731+3717 is originally associated with M15 at a confidence level of "seven nines". We find that such a high-velocity star ($V_{\rm ej} = 548^{+6}_{-5}$ km s$^{-1}$) was most likely tidally ejected from as close as one astronomical unit to the center of M15, confirming an IMBH ($\ge 100 M_{\odot}$ with a credibility of 98%) as the exclusive nature of the central unseen mass proposed previously.