Inferring the dense nuclear matter equation of state with neutron star tides

Pantelis Pnigouras,Andrea Passamonti,Nils Andersson

doi:10.1051/epjconf/202225807002

Abstract

During the late stages of a neutron star binary inspiral finite-size effects come into play, with the tidal deformability of the supranuclear density matter leaving an imprint on the gravitational-wave signal. As demonstrated in the case of GW170817—the first direct detection of gravitational waves from a neutron star binary—this can lead to strong constraints on the neutron star equation of state. As detectors become more sensitive, effects which may have a smaller influence on the neutron star tidal deformability need to be taken into consideration. Dynamical effects, such as oscillation mode resonances triggered by the orbital motion, have been shown to contribute to the tidal deformability, especially close to the neutron star coalesence, where current detectors are most sensitive. We calculate the contribution of the various stellar oscillation modes to the tidal deformability and demonstrate the (anticipated) dominance of the fundamental mode. We show what the impact of the matter composition is on the tidal deformability, as well as the changes induced by more realistic additions to the problem, e.g. the presence of an elastic crust. Finally, based on this formulation, we develop a simple phenomenological model describing the effective tidal deformability of neutron stars and show that it provides a surprisingly accurate representation of the dynamical tide close to merger.

Highlights

The breakthrough detections of gravitational waves from binary neutron star inspirals [1, 2] have led to renewed focus on the elusive neutron star equation of state
During the late stages of a neutron star binary inspiral finite-size e↵ects come into play, with the tidal deformability of the supranuclear density matter leaving an imprint on the gravitational-wave signal
As demonstrated in the case of GW170817—the first direct detection of gravitational waves from a neutron star binary—this can lead to strong constraints on the neutron star equation of state

Summary

Introduction

The breakthrough detections of gravitational waves from binary neutron star inspirals [1, 2] have led to renewed focus on the elusive neutron star equation of state. Much of the recent focus has been on the neutron star tidal deformability, essentially the extent to which the tidal interaction with a binary companion deforms the neutron star fluid. This is a useful measure as it can be extracted from (or, at least, constrained by) the gravitational-wave signal [3, 4]. As the star is deformed by the tidal interaction, matter is driven out of equilibrium and it is easy to argue that the relevant nuclear reactions are too slow to re-establish equilibrium on the time scale of inspiral. We outline the work presented in Refs. [15, 18, 19]

The effective Love number

Adding the crust

A phenomenological model

Findings

Implications