On the evolution and fate of supermassive stars

TL;DR

This paper models the evolution of supermassive stars with 60-1000 solar masses, predicting their end states as black holes or supernovae, and discusses implications for ultraluminous X-ray sources.

Contribution

It provides new stellar evolution models for supermassive stars, incorporating mass-loss prescriptions aligned with observed stellar properties.

Findings

Stars up to 1000 Msun end as objects less than 150 Msun.

Such stars likely collapse into black holes or explode as pair-instability supernovae.

Runaway stellar collisions are unlikely to produce intermediate-mass black holes in ULXs.

Abstract

We study the evolution and fate of solar composition supermassive stars in the mass range 60 - 1000 Msun. Our study is relevant both for very massive objects observed in young stellar complexes as well as supermassive stars that may potentially form through runaway stellar collisions. We predict the outcomes of stellar evolution employing a mass-loss prescription that is consistent with the observed Hertzsprung-Russell Diagram location of the most massive stars. We compute a series of stellar models with an appropriately modified version of the Eggleton evolutionary code. We find that super-massive stars with initial masses up to 1000 Msun end their lives as objects less massive than ~150 Msun. These objects are expected to collapse into black holes (with M < 70 Msun) or explode as pair-instability supernovae. We argue that if ultraluminous X-ray sources (ULXs) contain intermediate-mass black holes, these are unlikely to be the result of runaway stellar collisions in the cores of young clusters.