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

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 intersected that of globular cluster M15 within the cluster tidal radius. Both its metallicity [Fe/H] and alpha-to-iron abundance ratio [[Formula: see text]/Fe] are consistent with those of M15. Furthermore, its location falls right on the fiducial sequence of cluster M15 on the color-absolute magnitude diagram, suggesting similar ages. These findings support the notion that J0731+3717 was originally associated with M15 at a confidence level of 'seven nines'. We find that such a high-velocity star ([Formula: see text] km s[Formula: see text]) was most likely tidally ejected from as close as one astronomical unit to the center of M15, confirming an IMBH ([Formula: see text] with a credibility of 98%) as the exclusive nature of the central unseen mass proposed previously.