Statistics
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apjs..100..217i&link_type=abstract
Astrophysical Journal Supplement v.100, p.217
Statistics
47
Accretion, Accretion Disks, Stars: Binaries: Close, Stars: Evolution, Stars: Interiors, Stars: Statistics, X-Rays: Stars
Scientific paper
Using a numerical scenario code which is based on the current theory of stellar evolution and on a semiempirical birth function for binary stars, a model for the Galactic high-mass X-ray binary (HMXB) population is constructed. There is general agreement between predictions of the theoretical model and observed properties of HMXBs with respect to numbers and with respect to space velocity, mass, and orbital period distributions. Accretion by a close neutron star or black hole from the wind emitted by an OB star companion produces intense X-ray emission for 3 × l03-3 × l05 yr; the precise duration depends on the semimajor axis of the system and on the donor mass. The average HMXB lifetime is 14,000 yr. The model gives an HMXB birthrate ˜2.6 × l0-3 yr-1, with one out of 6-11 systems containing a black hole of mass ˜10 Msun. The total number of bright (LX > 1000 Lsun.) HMXBs is, according to the model, about 40, and the median peculiar velocity of these systems is ˜60 km s-1. Reasonable agreement with the observed distribution in number versus space velocity is achieved without invoking a "kick" other than the recoil velocity associated with mass loss in a supernova explosion.
Approximately 10% of all HMXBs with an OB star donor are predicted to evolve into close binaries with Wolf Rayet donors and with mass-exchange rates large enough to make them observable in X-rays throughout the Galaxy. Cyg X-3 is the only such system known. The discrepancy between observed and predicted numbers can possibly be ascribed, if the accretor is a neutron star, to a magnetic propeller mechanism which inhibits accretion, and, if the accretor is a black hole, to the absence of an accretion disk.
Following the HMXB phase, some systems evolve into very close binary black holes and neutron stars which merge under the influence of gravitational wave radiation. The merger rate of black holes in the Galaxy is estimated to be ˜2 × l0-4 yr-1, and the merger rate of neutron star pairs is estimated to be ˜3 × l0-5 yr-1. The volume of space that produces merger events which are potentially detectable as pulsed gravitational wave sources of large energy depends strongly on the masses of the merging components, and, if the black hole mass is taken to be ˜10 Msun, the frequency of detectable black hole mergers may be about 10 times larger then the frequency of detectable mergers of binary neutron stars.
Iben Icko Jr.
Tutukov Alexander V.
Yungelson Lev R.
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