Formation and evolution of primordial protostellar systems

Abstract

We present a suite of three-dimensional, moving mesh simulations that directly resolve the collapse of the gas beyond the formation of the first protostar at the center of a dark matter minihalo. In analogy to previous studies that employed sink particles, we find that the Keplerian disk around the primary protostar fragments into a number of secondary protostars, which is facilitated by H2 collisional dissociation cooling and collision-induced emission. The further evolution of the protostellar system is characterized by strong gravitational torques that transfer angular momentum between the secondary protostars formed in the disk and the surrounding gas. This leads to the migration of about half of the secondary protostars to the center of the cloud in a free-fall time, where they merge with the primary protostar and enhance its growth to about five times the mass of the second most massive protostar. By the same token, a fraction of the protostars obtain angular momentum from other protostars via N-body interactions and migrate to higher orbits. On average, only every third protostar survives until the end of the simulation. However, the number of protostars present at any given time increases monotonically, suggesting that the protostellar system will continue to grow beyond the limited period of time simulated.