2013MNRAS.430.1970H

We argue that one of the basic assumptions of the Bondi accretion process, that the accreting object has zero pressure, might not hold in many galaxies because of the pressure exerted by stellar winds of a star orbiting the central supermassive black hole (SMBH). Hence, the Bondi accretion cannot be used in these cases, such as in the galaxy NGC 3115. The winds of these high-velocity stars are shocked to temperatures above the virial temperature of the galaxy, leading to the formation of a hot bubble of size ∼ 0.1-10pc near the centre. This hot bubble can substantially reduce the mass accretion rate by the SMBH. If the density of the hot bubble is lower than that of the interstellar medium, a density-inversion layer is formed. As the gas loses energy by X-ray radiation, eventually more mass of the cooling shocked stellar winds will be accreted to the SMBH. This accretion will likely be of cold clumps. After a period of millions of years of low active galactic nucleus (AGN) activity, therefore, stronger AGN activity will occur that will heat and expel gas, much as in cooling-flow clusters. Adding to other problems of the Bondi process, our results render the Bondi accretion irrelevant for AGN feedback in cooling flow in galaxies and small groups of galaxies and during galaxy formation.