Galactic Center: Implications of recent Chandra observations for spherical accretion models of Sgr A*
At the centre of the Milky Way lurks a unique compact nonthermal radio source, Sgr A*. It is thought to be powered by a 2.6×106 solar mass black hole which is accreting the stellar winds from nearby early type stars such as IRS 16. Until recent high resolution Chandra observations, Sgr A* has never been unequivocably detected at wavelengths shorter than the submillimetre. However, the low X-ray luminosity of Sgr A*, as well as its spectral shape, has serious implications for applicable black hole accretion models. In particular, it suggests that the density of the accreting ambient medium, and consequently the mass accretion rate, is lower than that expected from hydrodynamical simulations as well as from observations of the mass-losing stars. We discuss such difficulties and present some possible solutions in the context of a quasi-spherical accretion model.