Universality in quasinormal modes of neutron stars with quark-hadron crossover

TL;DR

This paper investigates gravitational wave modes in neutron stars with quark-hadron crossover equations of state, revealing universal relations for the fundamental mode that can help distinguish different EOS types through stellar radii and deviations in pressure mode frequencies.

Contribution

It demonstrates that universal relations for $f$-mode frequencies remain valid for QHC EOS, enabling differentiation of EOS types via stellar radius evolution and pressure mode deviations.

Findings

$f$-mode frequencies are smaller with QHC EOS compared to hadronic EOS.

Universal relations for $f$-mode frequencies are preserved with QHC EOS.

Deviations in $p_1$-mode frequencies can distinguish QHC EOS from hadronic EOS.

Abstract

We examine the gravitational wave frequencies of the fundamental ($f$-) and 1st pressure ($p_1$-) modes excited in the neutron star models constructed with the quark-hadron crossover (QHC) type equations of state (EOS). We find that the $f$-mode frequencies with QHC EOS basically are smaller and the $p_1$-mode frequencies with QHC EOS are larger than those with hadronic EOS, focusing on the neutron star model with a fixed mass. We also find that the universality in the $f$-mode frequencies multiplied by the stellar mass as a function of the stellar compactness or as a function of the dimensionless tidal deformability, which is derived with various hadronic EOSs, can keep even with QHC EOS. That is, using these universal relations, one cannot distinguish QHC EOS from hadronic EOSs. Instead, using the relations one can extract the stellar radii whose evolution from low to high mass neutron stars can differentiate QHC from hadronic EOSs. On the other hand, we find that the $p_1$-mode frequencies multiplied by the stellar mass with QHC EOS significantly deviate in a certain mass range from the corresponding empirical relations derived with various hadronic EOSs, with which one may distinguish QHC EOS from hadronic EOSs.