Black hole with unusual mass discovered

Most known black holes are either extremely massive, like the supermassive black holes found at the cores of large galaxies, or relatively light, with masses less than 100 times that of the Sun. Intermediate black holes with masses of are surprisingly rare, that they are considered a “missing link” in the evolution of black holes since their creation.

Now, an international team of astronomers has used more than 500 images taken by the Hubble Space Telescope over two decades of observations to search for traces of the gravitational influence of intermediate-mass black holes.

In particular, it focused on carefully studying the motions of seven unusually fast-moving stars in the innermost region of the globular star cluster Omega Centauri.

These stars, by their motion, provide new and compelling evidence of the gravitational influence of the intermediate-mass black hole that attracts them. To date, only a few intermediate-mass black hole candidates have been discovered.

Omega Centauri is made up of about 10 million stars, held together by the gravitational influence they exert on each other. The cluster is about 10 times more massive than other large globular clusters and, in fact, is almost as massive as a small galaxy.

An international team led by Maximilian Heberle at the Max Planck Institute for Astronomy in Germany created a huge catalog of these stars’ motions by measuring the velocities of 1.4 million stars inferred from Hubble images of the cluster. Most of these observations were intended to calibrate Hubble’s instruments rather than for scientific use, but they turned out to be an ideal database for the team’s needs.

Heberle and his colleagues found seven stars that shouldn’t be there. These stars are moving so fast that they would normally escape the cluster and never return. The most likely explanation for this mystery is that a very massive object is gravitationally pulling on these stars and holding them close to the center. The only object that could be massive enough to do this is a black hole, in which case, judging by the amount of gravitational pull it exerts, it would be an intermediate-mass object, estimated to be just over 8,000 times the mass of the Sun.

The apparent location of the intermediate-mass black hole is circled in the center of the Omega Centauri sector image. The scale bar represents one-tenth of a light-year. (Image: ESA/Hubble/NASA/Maximilian Heberle/MPIA)

The study is called “Fast-moving stars around the intermediate-mass black hole in ω Centauri.” It was published in the academic journal Nature. (Fountain: NCYT by Amazings)