September 8, 2016

Hundreds of ‘impossible’ black holes found in globular cluster

Researchers from the University of Surrey have apparently done the impossible: they’ve used a series of advanced computer simulations to map a globular cluster called NGC 6101 and found that this spherical collection of stars likely contains several hundred black holes.

Writing in a recent edition of the journal Monthly Notices of the Royal Astronomical Society, the team mapped NGC 6101 and were able to deduce the existence of black holes within the system. Previous research had suggested that such a feat would have been impossible, as any black holes would have been expelled from the cluster in the aftermath of a supernova explosion.

“Due to their nature, black holes are impossible to see with a telescope, because no photons can escape,” lead author Miklos Peuten said in a statement. “In order to find them we look for their gravitational effect on their surroundings. Using observations and simulations we are able to spot the distinctive clues to their whereabouts and therefore effectively ‘see’ the un-seeable.”

“Our work is intended to help answer fundamental questions related to dynamics of stars and black holes, and the recently observed gravitational waves. These are emitted when two black holes merge, and if our interpretation is right, the cores of some globular clusters may be where black hole mergers take place,” added co-author Mark Gieles, a professor of astrophysics and a Royal Society University Research Fellow (URF) working at the university.

Findings could lead to discovery of even more black holes

It was only three years ago that astrophysicists first discovered individual black holes in globular clusters through a rare event in which the black hole receives material from a companion star, the researchers explained. Now, Peuten, Gieles and their colleagues have demonstrated that there is a good chance that NGC 6101 contains hundreds of the gravitationally-rich phenomena.

The Surrey-led team selected NGC 6101 because of recent research which suggested that it could have a different makeup than many globular clusters – specifically, that it appears to be young in contrast to the ages of the individual stars it contains, and that the core of the cluster looks as if it contains fewer observable stars than one would expect to find there.

Gieles, Peuten and their colleagues recreated every individual star and black hole in NGC 6101 using computer models, and used the simulation to mimic their behaviors. Their models showed how the cluster evolved over a 13 billion year period, and revealed the impact that large numbers of black holes would have had on the visible stars. Those effects matched observations of NGC 6101, they noted, and demonstrated that the apparent youth of the cluster was the direct result of its large black hole population.

“This research is exciting as we were able to theoretically observe the spectacle of an entire population of black holes using computer simulations,” said Peuten, who is a Ph. D. student at the university. “The results show that globular clusters like NGC 6101, which were always considered boring are in fact the most interesting ones, possibly each harboring hundreds of black holes. This will help us to find more black holes in other globular clusters in the universe.”


Image credit: NASA