Cyg X-3: a Galactic double black hole or black hole-neutron star
  progenitor
  There are no known 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 (WR) type companion. Based on a comprehensive analysis of
observational data, it was recently argued that Cyg X-3 harbors a 2-4.5 Msun BH
and a 7.5-14.2 Msun WR companion. We find that the fate of such a binary leads
to the prompt (<1 Myr) formation of a close BH-BH system for the high end of
the allowed WR mass (M_WR>13 Msun). For the low- to mid-mass range of the WR
star (M_WR=7-10 Msun) Cyg X-3 is most likely (probability 70%) disrupted when
WR 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 per
year, while it drops down to 0.1 per year for BH-NS systems. If Cyg X-3 in fact
hosts a low mass BH and massive WR star, it lends additional support for the
existence of BH-BH/BH-NS systems.
