Accretion Flows Around Black Holes

Abstract

Most accreting black holes emit a substantial fraction of their luminosity in hard X-rays/soft $\gamma$-rays of up to $\sim \mathrm{few}\times 100$ keV. The observations suggest that the radiating gas is very hot, $T>10^9$ K, and optically thin. Theoretical attempts to explain the observations are reviewed and unresolved issues are highlighted.

20 pages, 3 figures included, compressed uuencoded Postscript, Review talk at the conference on "Some Unsolved Problems in Astrophysics," Princeton, April 27-29, 1995. To appear in the Proceedings to be published by Princeton Univ. Press (editors, J. N. Bahcall & J. P. Ostriker)