Dynamical tides in neutron stars: The impact of the crust

TL;DR

This paper investigates how the elastic crust of neutron stars influences their dynamical tidal response during inspiral, revealing that certain modes can cause crust fracture before merger, with implications for gravitational wave signals.

Contribution

It extends the theoretical framework of neutron star tides to include crust elasticity and analyzes mode excitations and crust breaking during inspiral.

Findings

Fundamental mode dominates tidal response.

Crust may fracture during late inspiral due to mode excitation.

Interface modes can induce crust fracture earlier in inspiral.

Abstract

We consider the dynamical tidal response of a neutron star in an inspiralling binary, focussing on the impact of the star's elastic crust. Within the context of Newtonian gravity, we add the elastic aspects to the theoretical formulation of the problem and quantify the dynamical excitation of different classes of oscillation modes. The results demonstrate the expectation that the fundamental mode dominates the tidal response and show how the usual tidal deformability (and the Love number) emerge in the static limit. In addition, we consider to what extent the different modes may be excited to a level where the breaking strain of the crust would be exceeded (locally). The results show that the fundamental mode may fracture the crust during the late stages of inspiral. This is also the case for the first gravity mode, which reaches the breaking threshold in strongly stratified stars. In our models with a fluid ocean, interface modes associated with the crust-ocean transition may also induce crust fracture. If this happens it does so earlier in the inspiral, at a lower orbital frequency.