The Supersonic Project: Star Formation in Early Star Clusters without Dark Matter

The formation mechanism of globular clusters (GCs) has long been debated by astronomers. It was recently proposed that supersonically induced gas objects (SIGOs)-which formed in the early Universe due to the supersonic relative motion of baryons and dark matter at recombination-could be the progenitors of early GCs. In order to become GCs, SIGOs must form stars relatively efficiently despite forming outside of dark matter halos. We investigate the potential for star formation in SIGOs using cosmological hydrodynamic simulations, including the aforementioned relative motions of baryons and dark matter, molecular hydrogen cooling in primordial gas clouds, and explicit star formation. We find that SIGOs do form stars and that the nascent star clusters formed through this process are accreted by dark matter halos on short timescales (~a few hundred megayears). Thus, SIGOs may be found as intact substructures within these halos, analogous to many present-day GCs. From this result, we conclude that SIGOs are capable of forming star clusters with similar properties to globular clusters in the early Universe, and we discuss their detectability by upcoming JWST surveys.