An international team of experts from Europe and China has performed the first simulations of globular clusters with a million stars on the high-performance GPU cluster of the Max Planck Computing and Data Facility. These – up to now - largest and most realistic simulations can not only reproduce observed properties of stars in globular clusters at unprecedented detail but also shed light into the dark world of black holes. The computer models produce high quality synthetic data comparable to Hubble Space Telescope observations. They also predict nuclear clusters of single and binary black holes. The recently detected gravitational wave signal might have originated from a binary black hole merger in the center of a globular cluster.
It has been a long-standing challenge to follow the evolution of a massive globular cluster with self-consistent numerical simulations. For the first time a team led by international experts at MPA, the Chinese Academy of Sciences and Peking University has carried out the – up to now – most realistic simulations of the evolution of a globular cluster with initially one million stars orbiting in the tidal field of the Milky Way for about 12 billion years. The simulations carried out at the Hydra Supercomputer at the Max Planck Computing and Data Facility (MPCDF) as part of the international DRAGON project set a new standard in globular cluster modeling.
Fig. 4: Cumulative mass distribution of the stellar components depicted in Fig. 2. The center of the system is populated by black holes (black line), whereas the more extended distribution of low mass main sequence stars (cyan line) dominates the total mass. The dots represent the half-mass radius of the respective components. © MPA
The evolution of the stellar population of a globular cluster can now be followed in great detail through all its dynamical and stellar evolution phases, including the loss of stars in the tidal field of the Milky Way. The evolution of single and binary stars with a large range of masses (0.08 -100 solar masses) are followed through their major evolutionary phases (Fig. 2). The DRAGON simulations have also been used to prepare synthetic color magnitude diagrams (CMD) as observed by Hubble (Fig. 3).
In the DRAGON simulations the black holes – remnants of massive stars with masses of ten to fifty solar masses – form a dense nuclear cluster in the center of the system (Fig. 2, panel with white background). In classical astronomy this black hole cluster can only be observed indirectly by its gravitational influence on the luminous – and observable – stars. A few dozen black holes form binaries and lose energy by gravitational radiation, a process included in our simulations.
The DRAGON project: