An international team of astronomers including UQ astronomer Holger Baumgardt has announced new evidence for the existence of a middleweight black hole in space – the first black hole of its mass known to science.

So far all known black holes fall into two categories: small, stellar-mass black holes weighing a few times the mass of our sun, and supermassive black holes weighing millions or billions of times that. Astronomers have expected since a long time that intermediate-mass black holes weighing 100 to 10,000 times the mass of our sun also exist, but until now no conclusive proof of such middleweights has been found.

In a new study, published in Nature in Feb. 2017, astronomers have used the acceleration of pulsars in the globular cluster 47 Tucanae to investigate how the mass is distributed in the cluster and if there is a massive black hole in the centre of it. Pulsars are compact remnants of dead stars whose radio signals can easily be detected. The pulsars in 47 Tuc are flung around in the cluster about due to the gravitational influence of the other stars, but researchers found that some additional mass in the centre is necessary to explain their accelerations. When combined with the kinematics of the stars, the combined evidence suggests the presence of an intermediate-mass black hole of about 2200 solar masses within 47 Tucanae.

The fact this black hole had eluded detection for so long suggested black holes of similar masses could be hiding in other globular clusters.

More details can be found here.