On the formation and interaction of multiple supermassive stars in cosmological flows

Supermassive primordial stars with masses exceeding ∼ 10^5 M⊙ that form in atomically cooled halos are the leading candidates for the origin of high-redshift quasars with z > 6. Recent numerical simulations, however, find that multiple accretion disks can form within a halo, each of which can host a supermassive star. Tidal interactions between the disks can gravitationally torque gas onto their respective stars and alter their evolution. Later, when two satellite disks collide, the two stars can come into close proximity. This may induce additional mass exchange between them. We investigate the co-evolution of supermassive stars in atomically-cooled halos driven by gravitational interactions between their disks. We find a remarkable diversity of evolutionary outcomes. The results depend on these interactions and how the formation and collapse times of the stars in the two disks are correlated. They range from co-evolution as main sequence stars to main sequence – black hole pairs and black hole – black hole mergers. We examine the evolution of these secondary supermassive stars in detail and discuss the prospects for binary interactions on much smaller scales after the disks merge within their host halos.