Stellar winds near massive black holes – the case of the S-stars

20 Jan

[2016MNRAS.456.3645L]  Lützgendorf, N.; Helm, E. van der; Pelupessy, F. I.; Portegies Zwart, S.

The Galactic Centre provides a unique laboratory to study the interaction of a supermassive black hole (SMBH) with its gaseous and stellar environment. Simulations to determine the accretion of stellar winds from the surrounding O-stars on to the black hole have been performed earlier, but in those the presence of the S-star system was ignored. The S-stars are a group of young massive B-stars in relatively close orbits around the black hole. Here, we simulate those stars in order to study their contribution to the accretion rate, without taking the more distant and massive O-stars into account. We use the Astrophysical Multipurpose Software Environment to combine gravitational physics, stellar evolution and hydrodynamics in a single simulation of the S-stars orbiting the SMBH, and use this framework to determine the amount of gas that is accreted on to the black hole. We find that the accretion rate is sensitive to the wind properties of the S-stars (rate of mass-loss and terminal velocity). Our simulations are consistent with the observed accretion rate of the black hole only if the stars exhibit high wind mass-loss rates that are comparable with those of evolved 7-10 Myr old stars with masses of M = 19-25 M. This is in contrast with observations that have shown that these stars are rather young, main-sequence B-stars. We therefore conclude that the S-stars cannot account for the accretion rate alone.