Realistic Equations of State Informing Neutron Star Post-Merger Gravitational-Wave Frequencies

TL;DR

This paper uses realistic equations of state to predict the gravitational-wave frequencies from neutron star merger remnants, emphasizing the importance of broadband detectors for observing these signals.

Contribution

It introduces the use of realistic, thermally consistent equations of state to accurately compute post-merger gravitational-wave frequencies.

Findings

Peak frequency ranges from ~2.5 to 4 kHz.

Broadband observatories are necessary for detection.

KAGRA high-frequency design is well-suited for measurements.

Abstract

Binary neutron star mergers are thought to produce hot, rapidly rotating neutron stars with masses that can far exceed their Tolman-Oppenheimer-Volkoff mass. The gravitational-wave emission from such remnants provides a unique opportunity to measure the nuclear equation of state at densities and temperatures not available to terrestrial experiments. Current detector design is informed by gravitational-wave signals from general relativistic hydrodynamics simulations of neutron star mergers, typically with hybrid thermal treatments for the equation of state, where a cold equation of state is modified by adding a thermal component. We use realistic equations of state based on the relativistic mean field model with consistent treatment of thermal effects to compute the distribution of expected peak gravitational-wave frequencies. Marginalising over equation of state and progenitor neutron star masses, we show the peak frequency of emission ranges from $\sim2.5$ to 4 kHz. The width of this distribution suggests the need for broadband observatories with kHz sensitivity, and calls into question some of the so-called post-merger optimised configurations. We show the proposed KAGRA high-frequency design is well-suited to measuring post-merger remnants when compared to the KAGRA broadband design.