Rates and Characteristics of Intermediate-Mass-Ratio Inspirals Detectable by Advanced LIGO

Gravitational waves from the inspiral of a neutron star (NS) or stellarmass black hole (BH) into an intermediate-mass black hole (IMBH) with mass M ∼ 50M⊙ to 350M⊙ may be detectable by the planned advanced generation of ground-based gravitational-wave interferometers. Such intermediate mass ratio inspirals (IMRIs) are most likely to be found in globular clusters. We analyze four possible IMRI formation mechanisms: (i) hardening of a NS–IMBH or BH– IMBH binary via three body interactions, (ii) hardening via Kozai resonance in a hierarchical triple system, (iii) direct capture, and (iv) inspiral of a compact remnant from a tidally captured main-sequence star; we also discuss tidal effects when the inspiraling object is a neutron star. For each mechanism we predict the eccentricity distribution of the resulting IMRIs. We find that IMRIs will have largely circularized by the time they enter the sensitivity band of ground-based detectors. Hardening of a binary via three-body interactions, which is likely to be the dominant mechanism for IMRI formation, yields eccentricities under 10