Galactic double neutron stars as dual-line gravitational-wave sources: Prospects with LISA and Cosmic Explorer

TL;DR

This paper explores the potential of detecting dual-line gravitational waves from double neutron star systems with LISA and Cosmic Explorer, providing insights into neutron star physics and binary geometry.

Contribution

It introduces enhanced neutron star waveform models with higher-order parameters and estimates detection prospects for dual-line signals with upcoming GW detectors.

Findings

Approximately 6-22 dual-line sources could be detected by Cosmic Explorer.

Median SNR for these sources is around 20-30.

Relative measurement accuracy of neutron star moment of inertia is about 8%.

Abstract

Double neutron star (DNS) systems could serve as intriguing dual-line gravitational-wave (GW) sources, emitting both high- and low-frequency GWs, arising respectively from the asymmetric spinning bodies of individual neutron stars (NSs) and the binary orbital inspiral. Detecting such dual-line signals could provide novel perspectives on binary orbital geometry and NS internal physics. We expand upon previously calculated spinning NS waveforms by incorporating higher-order terms of NS structural parameters. A population simulation is performed for spinning NS components in DNS systems potentially detectable by the space-based Laser Interferometer Space Antenna (LISA). Based on 4-year LISA observation of 35 resolvable DNS systems under an optimistic scenario, we estimate that 6 (22) spinning NS components could be detected by the next-generation ground-based GW detector, Cosmic Explorer, under log-uniform (uniform) sampling of NS structural parameters. For these dual-line sources, the median signal-to-noise ratio achievable with Cosmic Explorer is approximately 20--30. Through the dual-line GW detection strategy, the relative measurement accuracy of the NS moment of inertia is estimated to be $\sim 8\%$.