Detectability of Sub-Solar Mass Neutron Stars Through a Template Bank Search

TL;DR

This paper assesses how finite size effects and lower merger frequencies affect the detectability of sub-solar mass neutron star binaries with current gravitational-wave detectors, highlighting significant sensitivity reductions.

Contribution

It quantifies the sensitivity loss when using black hole template banks for neutron star signals and provides a conservative upper limit on merger rates of sub-solar mass neutron star binaries.

Findings

Sensitivity loss can reach up to 78.4% for certain systems.

Finite size effects significantly impact detection sensitivity.

Results support dedicated searches for low-mass neutron star binaries.

Abstract

We study the detectability of gravitational-wave signals from sub-solar mass binary neutron star systems by the current generation of ground-based gravitational-wave detectors. We find that finite size effects from large tidal deformabilities of the neutron stars and lower merger frequencies can significantly impact the sensitivity of the detectors to these sources. By simulating a matched-filter based search using injected binary neutron star signals with tidal deformabilities derived from physically motivated equations of state, we calculate the reduction in sensitivity of the detectors. We conclude that the loss in sensitive volume can be as high as $78.4 \%$ for an equal mass binary system of chirp mass $0.17 \, \textrm{M}_{\odot}$, in a search conducted using binary black hole template banks. We use this loss in sensitive volume, in combination with the results from the search for sub-solar mass binaries conducted on data collected by the LIGO-Virgo observatories during their first three observing runs, to obtain a conservative upper limit on the merger rate of sub-solar mass binary neutron stars. Since the discovery of a low-mass neutron star would provide new insight into formation mechanisms of neutron stars and further constrain the equation of state of dense nuclear matter, our result merits a dedicated search for sub-solar mass binary neutron star signals.