Accretion Disk Evolution with Wind Infall. II. Results of Three‐dimensional Hydrodynamical Simulations with an Illustrative Application to Sagittarius A*

Abstract

In the first paper of this series, using analytic tools, we examined how the evolution and structure of a massive accretion disk may be influenced significantly by the deposition of mass and angular momentum by an infalling Bondi-Hoyle wind. Such a mass influx impacts the long-term behavior of the disk by providing additional sources of viscosity and heating. In this paper, we make a significant improvement over this earlier work by incorporating the results of three-dimensional hydrodynamical simulations of the large-scale accretion from an ambient medium into the disk evolution equations developed previously. We discuss in detail two models, one with the axis of the disk parallel to and the second with the axis oriented perpendicular to the large scale Bondi-Hoyle flow. We find that the mass inflow rate onto the disk within logarithmic annuli is roughly constant with radius and that the impacting wind carries much less specific angular momentum than Keplerian. We also find, in general, that the infrared spectrum of a wind-fed disk system is steeper than that of a Shakura-Sunyaev configuration, due mainly to the dissipation of the wind's kinetic energy at the disk's surface. In applying our results to the Galactic center black hole candidate Sgr A*, accreting from nearby stellar winds, we demonstrate that a high wind inflow rate of the order of 10-4 M☉ yr-1 cannot be incorporated into a fossil disk without a significant dissipation of kinetic energy at all radii. Such a high dissipation would violate current infrared and near-infrared limits on the observed spectrum of Sgr A*.