Probing the Equation of State of Nuclear Matter via Neutron Star Asteroseismology

TL;DR

This paper uses relativistic calculations of neutron star crust oscillations to connect observed flare frequencies with the nuclear symmetry energy, providing constraints on nuclear matter properties.

Contribution

It introduces a method to relate neutron star asteroseismology observations to the density dependence of nuclear symmetry energy, offering new constraints on nuclear matter equations of state.

Findings

Calculated torsional oscillation frequencies are sensitive to symmetry energy slope.

Identified the fundamental torsional mode with observed QPOs in giant flares.

Provided a lower limit of L ≈ 50 MeV for the symmetry energy slope.

Abstract

We general relativistically calculate the frequency of fundamental torsional oscillations of neutron star crusts, where we focus on the crystalline properties obtained from macroscopic nuclear models in a way depending on the equation of state of nuclear matter. We find that the calculated frequency is sensitive to the density dependence of the symmetry energy, but almost independent of the incompressibility of symmetric nuclear matter. By identifying the lowest-frequency quasi-periodic oscillation in giant flares observed from soft gamma-ray repeaters as the fundamental torsional mode and allowing for the dependence of the calculated frequency on stellar models, we provide a lower limit of the density derivative of the symmetry energy as $L\simeq 50$ MeV.