  The formation of low-mass X-ray binaries containing a rather massive (M >~ 7
\msun) black hole is problematic because in most recent stellar evolutionary
calculations the immediate progenitors of these black holes (Wolf-Rayet stars)
lose so much mass via their stellar wind that their final masses are well below
the observed black hole masses. We discuss the recently proposed solution that
these binaries are formed through case C mass transfer (i.e. mass transfer
after core helium burning is completed), avoiding a long Wolf-Rayet phase and
thus significant mass loss. We show that only some of the currently available
models for the evolution of massive stars allow this formation channel. We also
investigate the effect of the downward revised Wolf-Rayet mass-loss rate as is
suggested by observations, and conclude that in that case Wolf-Rayet stars end
their lives with significantly higher masses than previously found and may be
able to form a black holes.

Astrophysics