Detecting dark matter with extreme mass-ratio inspirals

TL;DR

This paper explores how gravitational wave signals from extreme mass-ratio inspirals can be used to detect and characterize dark matter halos around supermassive black holes, considering effects like dynamical friction and accretion.

Contribution

It introduces a method to estimate dark matter halo parameters from GW signals and analyzes how dynamical effects improve measurement accuracy.

Findings

Dark matter influences GW signals from EMRIs.

Dynamical friction and accretion help break parameter degeneracies.

Parameter measurement uncertainties decrease by about an order of magnitude with dynamical effects.

Abstract

Extreme mass ratio inspirals (EMRIs), where a small compact object inspiralls onto a supermassive black hole, are excellent sources for the space-based laser interferometer gravitational wave (GW) detectors. The presence of dark matter surrounding the supermassive black hole will influence the binary orbital evolution and emitted gravitational waveform. By direct observation of GW signals, we assess the detector's capability to detect whether an EMRI is immersed in a dark matter halo and to measure its characteristic spatial scale $a_0$ and mass $M_{\rm halo}$. Apart from the GW emission, the dynamical friction and accretion caused by the dark matter halo can also affect the dynamics of an EMRI, leaving detectable signatures in the emitted gravitational signal. We perform a Fisher-matrix error analysis to estimate the errors of parameters $a_0$ and $M_{\rm halo}$, as well as their correlation. The results show that the highly correlated parameters $a_0$ and $M_{\rm halo}$ deteriorate the detector's ability to measure dark matter even though the dephasing and mismatch between signals with and without dark matter indicate much difference. The effects of the dynamical friction and accretion can break possible degeneracies between parameters $a_0$ and $M_{\rm halo}$, thus greatly decreasing the uncertainty by about one order of magnitude.