The evolution of massive stars in the Small Magellanic Cloud

Abstract

Massive stars in the early universe are born with only a small amount of heavy elements (or, 'metals’). These metal-poor massive stars played a crucial role in shaping the galaxies in the early universe. They are also the progenitors of the most violent stellar transients, i.e., gamma-ray bursts, superluminous supernovae, and merging massive black holes. Given their short lifetimes, metal-poor massive stars in our Galaxy are long gone. Fortunately, the Small Magellanic Cloud (SMC), a satellite galaxy of the Milky Way, is metal-poor and actively forming massive stars.<br /> We perform a theoretical study of the evolution of massive stars in this one-of-a-kind environment. We constrain uncertain internal mixing processes, such as convection, semiconvection and rotationally induced mixing, through large grids of 1-D stellar evolution models computed with MESA. We find that efficient semiconvection is favorable for explaining the high hydrogen surface abundance of hot Wolf-Rayet stars, and the presence of blue supergiants in the SMC. At the same time, we derive tight upper and lower limits for the efficiency of convective overshooting.<br /> These results will help to provide more realistic binary evolution models for investigating gravitational wave progenitors, which will allow us to exploit the expected stream of new detections once LIGO restarts operation with enhanced sensitivity.