Accretion of cool stellar winds on to Sgr A*: another puzzle of the Galactic Centre?

Sgr A* is currently being fed by winds from a cluster of gravitationally bound young mass-losing stars. Using observational constraints on the orbits, mass-loss rates and wind velocities of these stars, we numerically model the distribution of gas in the ∼ 0.1–10 arcsec region around Sgr A*. We find that radiative cooling of recently discovered slow winds leads to the formation of many cool filaments and blobs, and to a thin and rather light accretion disc on a scale of about an arcsecond. The disc, however, does not extend all the way to our inner boundary. Instead, hot X-ray-emitting gas dominates the inner arcsecond. In our simulations, cool streams of gas frequently enter this region on low angular momentum orbits, and are then disrupted and heated up to the ambient hot gas temperature. The accreting gas around Sgr A* is thus two-phase, with a hot component, observable at X-ray wavelengths, and a cool component, which may be responsible for the majority of the time variability of Sgr A* emission on time-scales of 100–1000 yr. We obtain an accretion rate of a few ×10−6 M⊙ yr−1, consistent with Chandra estimates, but variable on time-scales even shorter than 100 yr. These results strongly depend on the chosen stellar orbits and wind parameters. Further observational input is thus key to a better modelling of the Sgr A* wind accretion.