Formation of Low-mass Black Hole X-ray Transients

Abstract

We study the formation of low-mass X-ray binaries with a black hole as accreting object. The performed semi-analytic analysis reveals that the formation rate of black holes in low-mass X-ray binaries is about two orders of magnitude smaller than that of systems with a neutron star as accretor. This is contradicted by the six observed systems, which are all transients, which suggest that the majority of these systems has not been seen jet. The birthrate for both type of objects are expected to be similar (for reviews see Cowley 1992, Tanaka & Lewin 1995). Solution of this conundrum requires either that stars with masses less than 20~\msun can evolve into black holes, or that stellar wind from a member of a binary is accompanied by a much larger loss of angular momentum than hitherto assumed.