Elusive mid-sized black hole spotted at centre of swallowed galaxy

WASHINGTON: Astronomers have scrutinized a cluster of stars that is the apparent remnant core of a relatively small galaxy that was swallowed by the sprawling Milky Way 8 to 10 billion years ago. What lurks at the center of this cluster has them excited.

The researchers said on Wednesday the unusual motion of seven stars in this cluster provides compelling evidence for the presence of an elusive mid-sized black hole at its heart.

These are bigger than the class of ordinary black holes formed in the implosion of a single star but smaller than the behemoths residing at the nucleus of most galaxies.

The cluster, called Omega Centauri, contains about 10 million stars. The black hole within it is at least 8,200 times as massive as our sun, the researchers said.

The supermassive black hole called Sagittarius A* at the center of the Milky Way possesses 4 million times the mass of the sun. And that is dwarfed by supermassive black holes billions of times the mass of the sun in other galaxies.

“There has been a long debate whether intermediate-mass black holes exist in general, and specifically in Omega Centauri, and our detection might help to resolve that debate,” said astronomer Maximilian Häberle of the Max Planck Institute for Astronomy in Germany, lead author of the study published in the journal Nature.