Radiating Bondi and Cooling Site Flows

Abstract: Steady accretion of a radiating gas onto a central mass point is described and compared to classic Bondi accretion. Radiation losses are essential for accretion flows to be observed. Unlike Bondi flows, radiating Bondi flows pass through a sonic point at a finite radius and become supersonic near the center. The morphology of all radiating Bondi flows is described by a single dimensionless parameter. In radiating Bondi flows the mass accretion rate varies approximately as the first power of the central mass -- this differs significantly from the quadratic dependence on the central mass in classical Bondi flows. Mass accretion rates onto galaxy or cluster-centered black holes estimated from traditional and radiating Bondi flows are significantly different. In radiating Bondi flows the gas temperature increases at large radii, as in the cores of many galaxy groups and clusters, allowing radiating Bondi flows to merge naturally with gas arriving from their cluster environments. Some radiating flows cool completely before reaching the center of the flow, and this also occurs in cooling site flows in which there is no central gravitating mass.