Black holes in X-ray binaries - Marginal existence and rotation reversals of accretion disks

Abstract

We adopt the hypothesis that black holes in X-ray binaries are accreting gas from an accretion disk fed by a stellar wind emanating from the primary. The formation of such a disk is found to be marginal in the case of a steady, spherically symmetric stellar wind and may be controlled by random fluctuations in the wind parameters. Such fluctuations may cause reversals in the rotation direction of the disk. Reversals in a disk around a rapidly rotating black hole lead to two distinct intensity states and may be associated with the two states observed for Cyg X-1. Subject headings: stars: binaries - stars: black holes - X-rays: sources