Observability of dynamical tides in merging eccentric neutron star binaries

TL;DR

This paper studies how dynamical tides in eccentric neutron star binaries affect gravitational wave signals, showing they can cause detectable phase shifts that reveal neutron star properties and nuclear physics insights.

Contribution

It introduces an analytic stochastic model for dynamical tides in eccentric binaries and demonstrates their impact on GW phase shifts and neutron star seismology.

Findings

Dynamical tides can cause >1% energy transfer at close pericenter distances.

GW phase shifts due to tides can be detectable with aLIGO at 40 Mpc.

Observation of phase shifts can measure neutron star f-mode frequencies and probe the equation of state.

Abstract

While dynamical tides only become relevant during the last couple of orbits for circular inspirals, orbital eccentricity can increase their impact during earlier phases of the inspiral by exciting tidal oscillations at each close encounter. We investigate the effect of dynamical tides on the orbital evolution of eccentric neutron star binaries using post-Newtonian numerical simulations and construct an analytic stochastic model that reproduces the numerical results. Our study reveals a strong dependence of dynamical tides on the pericenter distance, with the fractional energy transferred to dynamical tides over that dissipated in gravitational waves (GWs) exceeding $\sim1\%$ at separations $r_\mathrm{p}\lesssim50$ km for large eccentricities. We demonstrate that the effect of dynamical tides on orbital evolution can manifest as a phase shift in the GW signal. We show that the signal-to-noise ratio of the GW phase shift can reach the detectability threshold of $8$ with a single aLIGO detector at design densitivity for eccentric neutron star binaries at a distance of $40$ Mpc. This requires a pericenter distance of $r_\mathrm{p0}\lesssim68$ km ($r_\mathrm{p0}\lesssim76$ km) at binary formation with eccentricity close to $1$ for a reasonable tidal deformability and f-mode frequency of $500$ and $1.73$ kHz ($700$ and $1.61$ kHz), respectively. The observation of the phase shift will enable measuring the f-mode frequency of neutron stars independently from their tidal deformability, providing significant insights into neutron star seismology and the properties of the equation of state. We also explore the potential of distinguishing between equal-radius and twin-star binaries, which could provide an opportunity to reveal strong first-order phase transitions in the nuclear equation of state.