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

We present numerical simulations of stellar wind dynamics in the central parsec of the Galactic centre. We are particularly interested in accretion of gas on to Sgr A*, the super-massive black hole. Unlike our previous efforts, here we use the 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 disclike structure. The accretion flow circularisation radius is roughly unchaged, ∼ 5000 Schwarzschild radii. The accretion rate is dominated by a few close ‘slow wind stars’ (vw ≤ 750 kms −1), and is consistent with the Bondi estimate, but variable on timescales of tens to hundreds of years. This variability is due to the stochastic in-fall of cold clumps, as in earlier simulations, and to the eccentric orbits of stars. The present models fail to explain the higher 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.

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