Black Holes in Dense Star Clusters

Northwestern University, Evanston IL

Investigators

Abstract

Most stars form in dense clusters, the largest of which contain many millions of stars. Since star clusters can exist for many billions of years, they are believed to contain large numbers of compact objects, such as black holes and neutron stars that formed a long time ago as the remnants of dead massive stars. This research program at Northwestern University will use state-of-the-art supercomputer simulations to study the formation and evolution of these compact objects in a variety of star cluster environments. The main focus will be on the production of close binaries containing two black holes, which can eventually merge and produce potentially detectable bursts of gravitational waves. The development of parallel computing techniques and new algorithms will have broad relevance and be of interest to scientists outside of physics and astronomy. The astrophysics research will be student-oriented and senior students will help train new team members, including undergraduate students. Education and public outreach activities are also planned that will take advantage of the facilities at the Adler Planetarium in Chicago, and at Dearborn Observatory on the Northwestern University campus in Evanston. This project will address a number of key questions concerning the formation and dynamical evolution of compact objects (black holes and neutron stars) in dense star clusters. As they experience friction against the background of lighter stars, massive compact objects are expected to rapidly concentrate in the dense inner cores of clusters, where the rates of dynamical interactions are very high. These interactions can both produce binaries and tighten their orbits. In some cases, through successive mergers, perhaps helped by accretion of gas, an intermediate mass black hole could eventually be formed. Many of the objects formed by these processes are potential multi-messenger sources. The project will use a hybrid approach of combining Monte Carlo and N-body codes to optimize computing speed, accuracy and realism and overcome the dynamical range problem of simulating very large star clusters in which most of the interesting dynamics happens in a relatively small, high-density central region. A library of more than an thousand new cluster models will be made publicly available at the conclusion of the project.