On the Formation and Interaction of Multiple Supermassive Stars in Cosmological Flows

TL;DR

This paper explores how gravitational interactions between multiple supermassive stars in primordial halos influence their evolution, leading to diverse outcomes such as binary systems and mergers, which are relevant for understanding high-redshift quasars.

Contribution

It introduces a detailed investigation of the co-evolution of multiple supermassive stars driven by disk interactions in atomically cooled halos, revealing diverse evolutionary pathways.

Findings

Diverse evolutionary outcomes depend on disk interactions and formation timing.

Possible outcomes include co-evolving stars, star-black hole pairs, and black hole mergers.

Disk collisions can induce mass exchange and binary formation.

Abstract

Supermassive primordial stars with masses exceeding $\sim10^5\,M_{\odot}$ 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.