The Birth of Binary Direct-collapse Black Holes

Supermassive primordial stars forming during catastrophic baryon collapse in atomically cooling halos at z similar to 15-20 may be the origin of the first quasars in the universe. However, no simulation to date has followed the evolution of these halos at resolutions that are high enough or for times that are long enough to determine if collapse actually produces supermassive stars (SMSs). Here we report new cosmological simulations of baryon collapse in atomically cooled halos for times that are long enough for SMSs to form and die as direct-collapse black holes (DCBHs). We find that the high infall rates required to build up such stars persist until the end of their lives and could fuel the rapid growth of their BHs thereafter. Our simulations also demonstrate that binary and even small multiples of SMSs can form in low-spin and high-spin halos, respectively. This discovery raises the exciting possibility of detecting gravitational waves from DCBH mergers with LISA and tidal disruption events in the near-infrared with the James Webb Space Telescope and ground-based telescopes in the coming decade.