Contribution of High‐Mass Black Holes to Mergers of Compact Binaries

We consider the merging of high-mass black-hole binaries of the Cyg X-1 type,in which the O-star companion becomes a neutron star following a supernovaexplosion. Our estimated rate of mergers, $\sim 2\times 10^{-5} yr^{-1}$ forthe Galaxy, is relatively low because of the paucity of high-mass black holes.None the less, because of their high masses, these black-hole, neutron-starbinaries could contribute importantly to the merging sought by LIGO. Fromstellar evolutionary calculations including mass loss, we estimate that a ZAMSmass of $\sim 80 \msun$ is necessary before a high-mass black hole can resultin a massive binary. We estimate the detection rate for LIGO of high-mass blackhole neutron-star mergers to be a factor $\sim 40$ greater than that for binaryneutron stars. We suggest how our high cut-off mass can be reconciled with therequirements of nucleosynthesis, and show that a bimodal distribution withmasses of black holes can account, at least qualitatively, for the manytransient sources which contain high-mass black holes.Comment: 35 pages and 1 postscript figure, to be published in A&