Dynamics of Primordial Black Hole Clusters

Primordial black holes (PBHs) that form from the collapse of density perturbations are more clustered than the underlying density field. In this talk we examine the formation of bound systems of PBHs in the early universe. These would hypothetically be the earliest gravitationally collapsed structures, forming when the universe is still radiation dominated. Depending upon the size and occupation of the clusters, PBH merging and core collapse occurs before they would have otherwise evaporated due to Hawking evaporation, leaving behind larger PBHs. This talk summarizes the results of PRD 84, 124031 (2011).