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

TL;DR

This study simulates the S-stars near the Galactic center to assess their contribution to black hole accretion, revealing that their winds alone cannot explain observed accretion rates, suggesting additional sources are involved.

Contribution

It introduces a detailed simulation of S-star winds and their impact on black hole accretion, highlighting the limitations of S-stars as the sole source of accreted material.

Findings

Accretion rate depends on S-star wind properties.

High wind mass-loss rates are needed to match observed accretion.

S-stars alone cannot account for the black hole's accretion rate.

Abstract

The Galactic center 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 onto 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 Multi-purpose Software Environment (AMUSE) to combine gravitational physics, stellar evolution and hydrodynamics in a single simulation of the S-stars orbiting the supermassive black hole, and use this framework to determine the amount of gas that is accreted onto 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 massloss rates that are comparable with those of evolved 7-10 Myr old stars with masses of M=19-25 M_SUN. 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.