The pattern of accretion flow on to Sgr A

The material accreting on to Sgr A* most probably comes from the nearby stars. We analyse the pattern of this flow at distances of a fraction of a parsec, and we argue that the net angular momentum of this material is low but non-negligible, and the initially supersonic disc accretion changes into subsonic flow with constant angular momentum. Next, we estimate the flow parameters at a distance R BHL from the black hole, and we argue that for the plausible parameter range the accretion flow is non-stationary. The inflow becomes supersonic at a distance of ∼104 Rg , but the solution does not continue below the horizon and the material piles up forming a torus, or a ring, at a distance of a few, up to tens of Schwarzchild, radii. Such a torus is known to be unstable and may explain strong variability of the flow in Sgr A*. Our considerations show that the temporary formation of such a torus seems to be unavoidable. Our best-fitting model predicts a rather large accretion rate of around 4 × 10−6- M⊙-yr−1 directly on Sgr A*. We argue that magnetic fields in the flow are tangled, and this allows our model to overcome the disagreement with the Faraday rotation limits.