Astrophysical constraints on neutron star $f$-modes with a nonparametric equation of state representation

TL;DR

This paper uses a nonparametric approach to constrain neutron star $f$-mode frequencies based on multi-messenger observations, exploring their impact on gravitational-wave signals and resonance phenomena in binary mergers.

Contribution

It introduces a Gaussian process model for the dense-matter equation of state to infer $f$-mode frequencies and assesses their effects on gravitational-wave signals from neutron star mergers.

Findings

$f$-mode frequencies depend on neutron star mass with quantified uncertainties.

Resonance with orbital frequency possible in unequal-mass binary mergers.

Estimated tidal phase contribution at merger due to $f$-modes is approximately 7 radians.

Abstract

We constrain the fundamental-mode ($f$-mode) oscillation frequencies of nonrotating neutron stars using a phenomenological Gaussian process model for the unknown dense-matter equation of state conditioned on a suite of gravitational-wave, radio and X-ray observations. We infer the quadrupolar $f$-mode frequency preferred by the astronomical data as a function of neutron star mass, with error estimates that quantify the impact of equation of state uncertainty, and compare it to the contact frequency for inspiralling neutron-star binaries, finding that resonance with the orbital frequency can be achieved for the coalescences with the most unequal mass ratio. For an optimally configured binary neutron star merger, we estimate the gravitational waveform's tidal phasing due to $f$-mode dynamical tides as $7^{+2}_{-3}$ rad at merger. We assess prospects for distinguishing $f$-mode dynamical tides with current and future-generation gravitational-wave observatories.