Fast-moving stars around an intermediate-mass black hole in Omega Centauri

TL;DR

This study presents evidence for an intermediate-mass black hole in Omega Centauri by observing fast-moving stars whose velocities exceed the cluster's escape velocity, suggesting a black hole of at least 8,200 solar masses.

Contribution

First direct evidence of fast-moving stars indicating an intermediate-mass black hole in Omega Centauri, clarifying previous uncertainties about its central mass.

Findings

Fast-moving stars have velocities above the cluster's escape velocity.

The inferred black hole mass is at least 8,200 solar masses.

Supports the existence of intermediate-mass black holes in globular clusters.

Abstract

Black holes have been found over a wide range of masses, from stellar remnants with masses of 5-150 solar masses (Msun), to those found at the centers of galaxies with $M>10^5$ Msun. However, only a few debated candidate black holes exist between 150 and $10^5$ Msun. Determining the population of these intermediate-mass black holes is an important step towards understanding supermassive black hole formation in the early universe. Several studies have claimed the detection of a central black hole in $\omega$ Centauri, the Milky Way's most massive globular cluster. However, these studies have been questioned due to the possible mass contribution of stellar mass black holes, their sensitivity to the cluster center, and the lack of fast-moving stars above the escape velocity. Here we report observations of seven fast-moving stars in the central 3 arcseconds (0.08 pc) of $\omega$ Centauri. The velocities of the fast-moving stars are significantly higher than the expected central escape velocity of the star cluster, so their presence can only be explained by being bound to a massive black hole. From the velocities alone, we can infer a firm lower limit of the black hole mass of $\sim$8,200 Msun, making this a compelling candidate for an intermediate-mass black hole in the local universe.