Cyg X-3: a Galactic double black hole or black hole-neutron star progenitor

TL;DR

This paper analyzes Cyg X-3, suggesting it is a progenitor of double black hole or black hole-neutron star systems, with implications for gravitational wave detection rates and the existence of such compact binaries.

Contribution

It provides a comprehensive analysis indicating Cyg X-3's potential to evolve into a BH-BH or BH-NS system, highlighting the likelihood and formation scenarios based on observational data.

Findings

High probability of forming a close BH-BH system for massive WR stars.

70% chance of disruption if WR star ends as a supernova.

Estimated LIGO/VIRGO detection rate of 10 BH-BH mergers per year.

Abstract

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.