The latest supercomputer simulations have revealed that the Milky Way could be populated with many more ‘rogue’ black holes than had previously been expected. These black holes could be travelling across the galaxy at very high speeds, absorbing anything that crosses their path.
While scientists have observed supermassive black holes at the centre of galaxies and small black holes formed at the end of a star’s life, so far there has little observational evidence for medium-weight black holes that fit somewhere between the two extremes.
It had previously been assumed that these ‘intermediate mass’ black holes are hiding in large clusters of stars. However, new computational models performed by astronomers at the universities of Vanderbilt, Pennsylvania and Michigan in America, have shown that if these black holes collide and merge with other objects they receive a ‘kick’ that pushes them out of the cluster into the galaxy at speeds of up to 4,000km/s.
‘This is much higher than anyone predicted. Even the average kick velocity of 200km/s is extremely high when compared to the escape velocities of typical astronomical objects,’ says Kelly Holley-Bockelmann, an astronomer at Vanderbilt University.
The Milky Way contains around 200 globular clusters, but Holley-Bockelmann’s models show that most of the black holes will now have escaped and be roving the surrounding galaxy. ‘With our least conservative assumptions, less than two per cent of the globular clusters should contain intermediate mass black holes today,’ she says.