Exotic matter influence on the polar quasi-normal modes of neutron stars with equations of state satisfying the $2 M_{\odot}$ constraint

TL;DR

This study investigates how exotic matter like hyperons and quarks affects the polar quasi-normal modes of neutron stars, providing new universal relations that could help constrain their internal structure and equations of state.

Contribution

It introduces a novel method using Exterior Complex Scaling to analyze neutron star oscillations and derives equation-of-state independent relations between mode frequencies and damping times.

Findings

Phenomenological relations between mode frequencies and damping times and neutron star compactness.

New universal relations between w mode and f mode characteristics.

Influence of exotic matter on the quasi-normal mode spectrum.

Abstract

In this paper we analyze the quasi-normal mode spectrum of realistic neutron stars by studying the polar modes. In particular we study the spatial wI mode, the f mode, and the fundamental p mode. The study has been done for 15 different equations of state containing exotic matter and satisfying the $2 M_{\odot}$ constraint. Since f and p modes couple to matter perturbations, the influence of the presence of hyperons and quarks in the core of the neutron stars is more significant than for the axial component. We present phenomenological relations for the frequency and damping time with the compactness of the neutron star. We also consider new phenomenological relations between the frequency and damping time of the w mode and the f mode. These new relations are independent of the equation of state, and could be used to estimate the central pressure, mass or radius, and eventually constrain the equation of state of neutron stars. To obtain these results we have developed a new method based on the Exterior Complex Scaling technique with variable angle.