On the evolution an 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-circle dot. 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-circle dot end their lives as objects less massive than similar or equal to 150 M-circle dot. These objects are expected to collapse into black holes (with M less than or similar to 70 M-circle dot) or explode as pair-instability supernovae. Conclusions. We argue that if ultralmninous 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.