Until recently, the existence of a globular cluster of stars containing several hundred black holes was not thought to be possible. When stars orbit around a galactic center such as our Milky Way in a spherical collection, it is known as a globular cluster.
A team from the University of Surrey have now used advanced computer simulations to map a globular cluster known as NGC 6101. From the results of these simulations, they deduce that black holes could exist within the system. Black holes form in the gravitational collapse of huge stars at the end of their lives. Each of the black holes in the simulation is larger than the Sun by a few orders of magnitude. Scientists previously believed that during the death of a star, the supernova explosion would expel the black holes from their parent cluster.
Lead author Miklos Peuten from the University of Surrey, explains that since photons can’t escape from a black hole, they are impossible to see with a telescope. They can however be detected by looking for their gravitational effect on their surroundings. The team used simulations and observations to identify distinctive clues to the black holes’ location.
Old theories as to how black holes form have been overturned as recently as 2013. By observing rare phenomena in which a companion star contributes material to the black hole, astrophysicists found individual black holes in globular clusters. The work showing that several hundred black holes could exist in NGC 6101 was supported by the European Research Council (ERC).
Co-author Professor Mark Gieles, from the University of Surrey notes that the intention of this work is to help answer important questions related to recently observed gravitational waves and the dynamics of black holes and stars. When two black holes merge, gravitational waves are released. If the conclusions drawn by the team is correct, black hole mergers take place in the cores of some globular clusters.
NGC 6101 is dynamically young in contrast to the ages of the individual stars when compared to other globular clusters. This distinctive makeup was only discovered recently and it suggests that NGC 6101 could be different to other clusters. These factors prompted the researchers to map this particular ancient globular cluster. The cluster also appears to be inflated with the core being under-populated by stars that can be observed.
NGC 6101 is thirteen billion years old and the team tracked the evolution and behavior of every individual star and black hole in the cluster with computer simulations. This showed the effects of big numbers of black holes on the visible stars. The researchers concluded from this that the unexplained dynamical apparent youth is caused by the large black hole population.
Peuten is exited that they were able to observe the spectacle of an entire population of black holes theoretically and is sure that these results will help researchers find more black holes in other globular clusters in the Universe. Each globular clusters like NGC 6101 could possibly be hiding hundreds of black holes, which makes globular clusters interesting and not as boring as they were previously considered.
Study has been published in the journal Monthly Notices of the Royal Astronomical Society.