Nonradial oscillations of quark stars

TL;DR

This paper investigates nonradial oscillations of quark stars, deriving empirical relations for gravitational wave frequencies that could help determine their internal properties and equation of state through observations.

Contribution

It provides the first detailed analysis of nonradial oscillation modes of quark stars, including new empirical formulas linking gravitational wave frequencies to stellar parameters.

Findings

The $f$-mode frequency strongly depends on the bag constant and stellar radius.

A new empirical formula relates $f$-mode frequency to the quark star's equation of state.

Observation of gravitational waves from these modes can probe quark star properties.

Abstract

Recently, it has been reported that a candidate for a quark star may have been observed. In this article, we pay attention to quark stars with radiation radii in the reported range. We calculate nonradial oscillations of $f$-, $w$- and $w_{\rm II}$-modes. Then, we find that the dependence of the $f$-mode quasi-normal frequency on the bag constant and stellar radiation radius is very strong and different from that of the lowest $w_{\rm II}$-mode quasi-normal frequency. Furthermore we deduce a new empirical formula between the $f$-mode frequency of gravitational waves and the parameter of the equation of state for quark stars. The observation of gravitational waves both of the $f$-mode and of the lowest $w_{\rm II}$-mode would provide a powerful probe for the equation of state of quark matter and the properties of quark stars.