Cyg X-3: A galactic double black hole or black-hole-neutron-star progenitor

There are no known stellar-origin double black hole (BH-BH) or black-hole-neutron-star (BH-NS) systems. We argue that Cyg X-3 is a very likely BH-BH or BH-NS progenitor. This Galactic X-ray binary consists of a compact object, wind-fed by a Wolf-Rayet (W-R) type companion. Based on a comprehensive analysis of observational data, it was recently argued that Cyg X-3 harbors a 2-4.5 M ☉ black hole (BH) and a 7.5-14.2 M ☉ W-R companion. We find that the fate of such a binary leads to the prompt (lsim 1 Myr) formation of a close BH-BH system for the high end of the allowed W-R mass (M W-R gsim 13 M ☉). For the low- to mid-mass range of the W-R star (M W-R ~ 7-10 M ☉) Cyg X-3 is most likely (probability 70%) disrupted when W-R ends up as a supernova. However, with smaller probability, it may form a wide (15%) or a close (15%) BH-NS system. The advanced LIGO/VIRGO detection rate for mergers of BH-BH systems from the Cyg X-3 formation channel is ~10 yr–1, while it drops down to ~0.1 yr–1 for BH-NS systems. If Cyg X-3 in fact hosts a low-mass black hole and massive W-R star, it lends additional support for the existence of BH-BH/BH-NS systems