Forming short-period Wolf-Rayet X-ray binaries and double black holes through stable mass transfer

We show that black hole high-mass X-ray binaries (HMXBs) with O- orB-type donor stars and relatively short orbital periods, of order oneweek to several months may survive spiral-in, to then form Wolf-Rayet(WR) X-ray binaries with orbital periods of order a day to a few days;while in systems where the compact star is a neutron star, HMXBs withthese orbital periods never survive spiral-in. We therefore predict thatWR X-ray binaries can only harbour black holes. The reason why blackhole HMXBs with these orbital periods may survive spiral-in is: thecombination of a radiative envelope of the donor star and a high mass ofthe compact star. In this case, when the donor begins to overflow itsRoche lobe, the systems are able to spiral in slowly with stable Rochelobe overflow, as is shown by the system SS433. In this case, thetransferred mass is ejected from the vicinity of the compact star(so-called isotropic re-emission mass-loss mode, or SS433-likemass-loss), leading to gradual spiral-in. If the mass ratio of donor andblack hole is ≳3.5, these systems will go into common-envelopeevolution and are less likely to survive. If they survive, they produceWR X-ray binaries with orbital periods of a few hours to one day.Several of the well-known WR+O binaries in our Galaxy and the MagellanicClouds, with orbital periods in the range between a week and severalmonths, are expected to evolve into close WR-black hole binaries, whichmay later produce close double black holes. The galactic formation rateof double black holes resulting from such systems is still uncertain, asit depends on several poorly known factors in this evolutionary picture.It might possibly be as high as ˜10-5 yr-1