Variable accretion and emission from the stellar winds in the Galactic centre

TL;DR

This study uses advanced simulations with updated stellar wind data to analyze gas accretion onto Sgr A* in the Galactic centre, revealing variable accretion rates influenced by stellar orbits and wind properties.

Contribution

The paper introduces new simulations incorporating recent observational data on stellar orbits and wind velocities, improving understanding of gas dynamics near Sgr A*.

Findings

Accretion rate is dominated by slow wind stars with v_w < 750 km/s.

Accretion variability occurs on timescales of tens to hundreds of years.

Models do not fully explain past high luminosity of Sgr A*, but suggest possible causes.

Abstract

We present numerical simulations of stellar wind dynamics in the central parsec of the Galactic centre, studying in particular the accretion of gas on to Sgr A*, the super-massive black hole. Unlike our previous work, here we use state-of-the-art observational data on orbits and wind properties of individual wind-producing stars. Since wind velocities were revised upwards and non-zero eccentricities were considered, our new simulations show fewer clumps of cold gas and no conspicuous disc-like structure. The accretion rate is dominated by a few close `slow wind stars' v_w < 750 km/s, and is consistent with the Bondi estimate, but variable on time-scales of tens to hundreds of years. This variability is due to the stochastic in-fall of cold clumps of gas, as in earlier simulations, and to the eccentric orbits of stars. The present models fail to explain the high luminosity of Sgr A* a few hundred years ago implied by Integral observations, but we argue that the accretion of a cold clump with a small impact parameter could have caused it. Finally, we show the possibility of constraining the total mass-loss rate of the `slow wind stars' using near infra-red observations of gas in the central few arcseconds.