On the evolution and fate of super-massive stars

Context.We study the evolution and fate of solar composition super-massive stars in the mass range 60–1000 $M_{\odot}$. Our study is relevant for very massive objects observed in young stellar complexes as well as for super-massive stars that could potentially form through runaway stellar collisions. Aims.We predict the outcomes of stellar evolution by employing a mass-loss prescription that is consistent with the observed Hertzsprung-Russell Diagram location of the most massive stars. Methods.We compute a series of stellar models with an appropriately modified version of the Eggleton evolutionary code. Results.We find that super-massive stars with initial masses up to 1000 $M_{\odot}$ end their lives as objects less massive than $\simeq$150 $M_{\odot}$. These objects are expected to collapse into black holes (with $M \la 70 \mbox {~$M_{\odot}$}$) or explode as pair-instability supernovae. Conclusions.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