Unified description of accretion flows around black holes

Feb, 1995
11 pages
Published in:
  • Astrophys.J.Lett. 443 (1995) L61
e-Print:
Report number:
  • ASTRO-1995-01,
  • CFA-4046

Citations per year

19952002200920162023051015
Abstract: (arXiv)
We provide a unified description of thermal equilibria of black hole accretion disks, including the newly-discovered advection-dominated solutions. We classify the solutions on the basis of optical depth and importance of advection cooling. We demonstrate that only four physically distinct topological types of equilibria exist. Two of the types correspond to optically thin and optically thick equilibria, while the other two types are distinguished by whether advection is negligible or dominant. A stable Shakura-Sunyaev disk exists only for accretion rates M˙\dot M below a certain maximum. However, there is a critical viscosity parameter αcrit\alpha_{\rm crit}, which is a function of radius, such that for α>αcrit\alpha>\alpha_{\rm crit} advection-dominated solutions exist for all M˙\dot M. Even when α<αcrit\alpha< \alpha_{\rm crit}, the advection-dominated solutions are available for a wide range of M˙\dot M except for a gap around the Eddington rate. We therefore suggest that advection-dominated flows may be more common than standard thin disks in black hole systems. For certain ranges of radii and M˙\dot M, no stable steady state solution is possible. In these cases, we suggest that limit cycle behavior may occur, leading to variability.