Detection of Intermediate-Mass Ratio Inspirals in Globular Clusters: Revealing the Brownian Motion with Gravitational Waves

TL;DR

This paper investigates the detectability of intermediate-mass ratio inspirals in globular clusters by future GW observatories, emphasizing the importance of modeling their Brownian motion to accurately interpret signals and study their environment.

Contribution

It models the Brownian motion of IMRIs and assesses its impact on GW detection and parameter estimation, highlighting the need to include environmental effects in waveform analysis.

Findings

Less than 10% of IMRIs will have high SNR detections.

Detected signals will often show discernible Brownian motion effects.

Ignoring Brownian motion can lead to mismatched waveform models.

Abstract

Intermediate-mass ratio inspirals (IMRIs) formed by stellar-mass compact objects orbiting intermediate-mass black holes will be detected by future gravitational wave (GW) observatories like TianQin, LISA, and AION. We study a set of 100 IMRI systems in globular clusters obtained from MOCCA simulations to estimate their detectability. Furthermore, we model the Brownian motion of the IMRIs induced by weak interactions with the surrounding field of stars and include its effect on the GW's phase through Doppler and aberrational phase shift. We find that a small fraction of IMRIs ($<10\,\%$) will have signal-to-noise ratios (SNR) high enough to be detected by TianQin, LISA, and AION. However, for all sources detected, the SNR is high enough to discern the Brownian motion of the IMRI. More precisely, we find that the match between the signal containing the effect of the Brownian motion and a waveform model without this effect is mostly low ($<0.8$). These results highlight the importance of including the interaction of IMRIs with the surrounding field of stars to obtain proper detection, but also show the possibility of studying the environment of the source using GWs.