Anomalies in Time Delays of Lensed Gravitational Waves and Dark Matter Substructures

TL;DR

This paper proposes using time delay measurements of lensed gravitational waves from third-generation detectors, combined with electromagnetic observations, as a novel and precise method to detect dark matter substructures in galaxies, addressing discrepancies in dark matter predictions.

Contribution

It introduces a new approach leveraging lensed gravitational waves for dark matter substructure detection, potentially offering higher accuracy than traditional methods.

Findings

Lensed GW signals can detect dark matter substructures at several percent levels.

Combining GW and electromagnetic data improves detection accuracy.

Dark matter substructure effects are measurable with current and future GW detectors.

Abstract

The cold dark matter scenario of hierarchical large-scale structure formation predicts the existence of abundant subhalos around large galaxies. However, the number of observed dwarf galaxies is far from this theoretical prediction, suggesting that most of the subhalos could be dark or quite faint. Gravitational lensing is a powerful tool to probe the mass distribution directly irrespective of whether it is visible or dark. Time delay anomalies in strongly lensed quasar systems are complementary to flux ratio anomalies in probing dark matter substructure in galaxies. Here we propose that lensed gravitational waves detected by the third-generation ground detectors with quite accurate time delay measurements could be a much better tool for this study than conventional techniques. Combined with good quality images of lensed host galaxies identified by the electromagnetic counterpart measurements, lensed GW signals could make the systematic errors caused by dark matter substructures detectable at several percent levels, depending on their mass functions, internal distribution of subhalos and lensing system configuration.