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

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 [α/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 5.4σ. We find that such a high-velocity star (V_ 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 (≥ 100 M_⊙ with a credibility of 98 exclusive nature of the central unseen mass proposed previously.