The Effect of Massive Perturbers on Extreme Mass-Ratio Inspiral Waveforms

TL;DR

This paper investigates how a nearby supermassive black hole can perturb gravitational wave signals from extreme mass-ratio inspirals, potentially allowing detection and characterization of such perturbers through waveform deviations.

Contribution

It introduces the concept that a second supermassive black hole within a few tenths of a parsec can cause detectable waveform deviations in EMRI signals, enabling new probes of merger environments.

Findings

Perturbers cause systematic waveform deviations detectable in EMRI signals.

Higher derivatives of motion can reveal the mass and distance of the perturber.

A second supermassive black hole within 0.1 parsecs can be identified through waveform analysis.

Abstract

Extreme mass ratio inspirals, in which a stellar-mass object merges with a supermassive black hole, are prime sources for space-based gravitational wave detectors because they will facilitate tests of strong gravity and probe the spacetime around rotating compact objects. In the last few years of such inspirals, the total phase is in the millions of radians and details of the waveforms are sensitive to small perturbations. We show that one potentially detectable perturbation is the presence of a second supermassive black hole within a few tenths of a parsec. The acceleration produced by the perturber on the extreme mass-ratio system produces a steady drift that causes the waveform to deviate systematically from that of an isolated system. If the perturber is a few tenths of a parsec from the extreme-mass ratio system (plausible in as many as a few percent of cases) higher derivatives of motion might also be detectable. In that case, the mass and distance of the perturber can be derived independently, which would allow a new probe of merger dynamics.