THE FATE OF Cyg X-1: AN EMPIRICAL LOWER LIMIT ON BLACK-HOLE-NEUTRON-STAR MERGER RATE
- Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw (Poland)
- Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States)
The recent distance determination allowed precise estimation of the orbital parameters of Cyg X-1, which contains a massive 14.8 M{sub Sun} black hole (BH) with a 19.2 M{sub Sun} O star companion. This system appears to be the clearest example of a potential progenitor of a black hole + neutron star (BH-NS) system. We follow the future evolution of Cyg X-1, and show that it will soon encounter a Roche lobe overflow episode, followed shortly by a Type Ib/c supernova and the formation of a neutron star (NS). It is demonstrated that in majority of cases ({approx}> 70%) the supernova and associated natal kick disrupt the binary due to the fact that the orbit expanded significantly in the Roche lobe overflow episode. In the reminder of cases ({approx}< 30%) the newly formed BH-NS system is too wide to coalesce in the Hubble time. Only sporadically ({approx}1%) may a Cyg X-1-like binary form a coalescing BH-NS system given a favorable direction and magnitude of the natal kick. If a Cyg X-1-like channel (comparable mass BH-O star bright X-ray binary) is the only or dominant way to form BH-NS binaries in the Galaxy, then we can estimate the empirical BH-NS merger rate in the Galaxy at the level of {approx}0.001 Myr{sup -1}. This rate is so low that the detection of BH-NS systems in gravitational radiation is highly unlikely, generating Advanced LIGO/VIRGO detection rates at the level of only {approx}1 per century. If BH-NS inspirals are in fact detected, it will indicate that the formation of these systems proceeds via some alternative and yet unobserved channels.
- OSTI ID:
- 22047365
- Journal Information:
- Astrophysical Journal Letters, Vol. 742, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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