Stellar winds pump the heart of the Milky Way

The central super-massive black hole of the Milky Way, Sgr A*, accretes at a very low rate making it a very underluminous galactic nucleus. Despite the tens of Wolf-Rayet stars present within the inner parsec supplying $\sim {10}^{-3}{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$ in stellar winds, only a negligible fraction of this material ($<{10}^{-4}$) ends up being accreted onto Sgr A*. The recent discovery of cold gas ($\sim {10}^4\mathrm{K}$) in its vicinity raised questions about how such material could settle in the hostile (${\sim}10^7\rm
K$) environment near Sgr A*. In this work we show that the system of mass-losing stars blowing winds can naturally account for both the hot, inefficient accretion flow, as well as the formation of a cold disk-like structure. We run hydrodynamical simulations using the grid-based code Ramses starting as early in the past as possible to observe the state of the system at the present time. Our results show that the system reaches a quasi-steady state in about $\sim 500\mathrm{y}\mathrm{r}$ with material being captured at a rate of $\sim {10}^{-6}{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$ at scales of $\sim {10}^{-4}\mathrm{p}\mathrm{c}$, consistent with the observations and previous models. However, on longer timescales ($\gtrsim 3000\mathrm{y}\mathrm{r}$) the material accumulates close to the black hole in the form of a disk. Considering the duration of the Wolf-Rayet phase ($\sim {10}^5\mathrm{y}\mathrm{r}$), we conclude that this scenario likely has already happened, and could be responsible for the more active past of Sgr A*, and/or its current outflow. We argue that the hypothesis of the mass-losing stars being the main regulator of the activity of the black hole deserves further consideration.