Numerical Simulations of Runaway Star Growth in Globular Clusters

Abstract

Understanding the early seeds of supermassive black holes remains a challenging, open question in theoretical astronomy. Repeated and rapid collisions in some globular clusters occurring in the first few million years after cluster formation have the potential to form very massive stars which then collapse to become massive black holes. In turn, these massive black holes serve as seeds of supermassive black holes powering luminous quasars observed at the epoch of reionization. We perform 23 numerical simulations of stellar dynamics and collisions within globular clusters of varying masses, radii, and concentrations. Although our simulations have not yet run far enough to cover the entire lifespan of most collisional clusters due to computational constraints, they show repeated collisions can form stars with several thousand solar masses on timescales of fewer than 3 Myr. Thus, we believe this formation scenario provides a promising pathway for very massive star formation. Further exploration of various cluster parameters and timescales to generate stars above 104 M is warranted.