Several candidates for binary BH with optical companions are known at present (see van Paradijs and McClintock, 1993, for a review). They must be products of the evolution of binary systems with massive companions. Lipunov et al. (1994b) calculated the expected number of BH+PSR binaries following directly from the modern scenario of binary star evolution using the Scenario Machine.
In the case of BH which are free of the complicated and poorly understood spin evolution connected with magnetic fields, etc., estimations of such types seem to be more reliable and parameter independent. We have found that our results depend sensitively only on two parameters fundamental for stellar evolution theory: the critical mass of the presupernova star that collapses directly to the BH, , and the fraction of the presupernova mass ( ) collapsing to the BH, . Using existing observational data, we place some restrictions on these parameters. We also estimate the number of BH arising as a result of AIC of NS.