Hydrodynamic simulations of the inner accretion flow of Sagittarius A* fuelled by stellar winds

We present athena++ grid-based, hydrodynamic simulations of accretion on to Sagittarius A* via the stellar winds of the ∼30 Wolf–Rayet stars within the central parsec of the galactic centre. These simulations span ∼4 orders of magnitude in radius, reaching all the way down to 300 gravitational radii of the black hole, ∼32 times further than in previous work. We reproduce reasonably well the diffuse thermal X-ray emission observed by Chandra in the central parsec. The resulting accretion flow at small radii is a superposition of two components: (1) a moderately unbound, sub-Keplerian, thick, pressure-supported disc that is at most (but not all) times aligned with the clockwise stellar disc, and (2) a bound, low-angular momentum inflow that proceeds primarily along the southern pole of the disc. We interpret this structure as a natural consequence of a few of the innermost stellar winds dominating accretion, which produces a flow with a broad distribution of angular momentum. Including the star S2 in the simulation has a negligible effect on the flow structure. Extrapolating our results from simulations with different inner radii, we find an accretion rate of approximately a few ×10−8 M⊙ yr−1 at the horizon scale, consistent with constraints based on modelling the observed emission of Sgr A*. The flow structure found here can be used as more realistic initial conditions for horizon scale simulations of Sgr A*.

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