Gravitational waves from intermediate-mass-ratio inspirals for ground-based detectors

TL;DR

This paper assesses the potential of Advanced LIGO to detect gravitational waves from intermediate-mass-ratio inspirals, exploring their wave characteristics, event rates, and how these signals can reveal the nature of the central massive object.

Contribution

It introduces a framework for using gravitational wave signals to map the central body's metric and distinguish black holes from other compact objects.

Findings

Estimated event rate of 10-30 per year for IMRIs.

Waveforms are likely tri-periodic if the central body is not a black hole.

Advanced LIGO can constrain deviations from Kerr black holes.

Abstract

We explore the prospects for Advanced LIGO to detect gravitational waves from neutron stars and stellar mass black holes spiraling into intermediate-mass ($M\sim 50 M_\odot$ to $350 M_\odot$) black holes. We estimate an event rate for such \emph{intermediate-mass-ratio inspirals} (IMRIs) of up to $\sim 10$--$30 \mathrm{yr}^{-1}$. Our numerical simulations show that if the central body is not a black hole but its metric is stationary, axisymmetric, reflection symmetric and asymptotically flat then the waves will likely be tri-periodic, as for a black hole. We report generalizations of a theorem due to Ryan (1995) which suggest that the evolutions of the waves' three fundamental frequencies and of the complex amplitudes of their spectral components encode (in principle) a full map of the central body's metric, full details of the energy and angular momentum exchange between the central body and the orbit, and the time-evolving orbital elements. We estimate that Advanced LIGO can measure or constrain deviations of the central body from a Kerr black hole with modest but interesting accuracy.