Incidence of coexisting massive black-hole pairs and nuclear compact binaries

Determine the incidence of the coexistence of a massive black-hole pair and a nuclear neutron-star-containing compact-binary population in galactic nuclei, in order to constrain the occurrence frequency of the proposed binary-ejection channel.

Background

The proposed slingshot mechanism requires a massive black-hole pair—comprising the central supermassive black hole and an intermediate-mass or secondary supermassive black hole—to coexist with a population of neutron-star-containing compact binaries in the nuclear region of a galaxy. The paper calculates the ejection efficiency, merger offsets, and phenomenologically normalized rates under this assumed configuration, but does not establish how frequently the required configuration occurs in real galaxies.

The unresolved incidence depends on the formation and evolution of massive black-hole pairs, the delivery and retention of compact binaries in galactic nuclei, and their joint dynamical evolution. Establishing this incidence would allow the channel’s absolute cosmological event rate to be compared quantitatively with the observed population of extreme-offset gamma-ray bursts and related transients.