Probing neutron stars with the full pre-merger and post-merger gravitational wave signal from binary coalescences

TL;DR

This paper develops a hybrid analysis method to utilize the entire gravitational wave signal from neutron star mergers, aiming to extract detailed information about neutron star internal structure and post-merger physics.

Contribution

It introduces a combined analytical and morphology-independent approach to analyze pre- and post-merger signals without artificial separation, enhancing neutron star physics insights.

Findings

Successfully reconstructs full signals in simulations

Estimates pre-merger tidal deformation and post-merger frequencies

Demonstrates potential to probe neutron star internal physics

Abstract

The gravitational wave signal emitted during the coalescence of two neutron stars carries information about the stars' internal structure. During the long inspiral phase the main matter observable is the tidal interaction between the binary components, an effect that can be parametrically modeled with compact-binary solutions to General Relativity. After the binary merger the main observable is frequency modes of the remnant, most commonly giving rise to a short-duration signal accessible only through numerical simulations. The complicated morphology and the decreasing detector sensitivity in the relevant frequencies currently hinder detection of the post-merger signal and motivate separate analyses for the pre-merger and post-merger data. However, planned and ongoing detector improvements could soon put the post-merger signal within reach. In this study we target the whole pre-merger and post-merger signal without an artificial separation at the binary merger. We construct a hybrid analysis that models the inspiral with templates based on analytical calculations and calibrated to numerical relativity and the post-merger signal with a flexible morphology-independent analysis. Applying this analysis to GW170817 we find, as expected, that the post-merger signal remains undetected. We further study simulated signals and find that we can reconstruct the full signal and simultaneously estimate both the pre-merger tidal deformation and the post-merger signal frequency content. Our analysis allows us to study neutron star physics using all the data available and directly test the pre-merger and post-merger signal for consistency thus probing effects such as the onset of the hadron-quark phase transition.