Rescaling strange-cluster stars and its implications on gravitational-wave echoes

TL;DR

This paper introduces a dimensionless rescaling method for strangeon stars, revealing their potential to produce gravitational-wave echoes with frequencies ranging from about 8 kHz to 100 Hz, depending on parameters.

Contribution

It develops a simple rescaling scheme for strangeon stars, reducing degrees of freedom and analyzing their gravitational-wave echo frequencies.

Findings

Strangeon stars can have photon spheres enabling GW echoes.

Minimum GW echo frequency is approximately 8 kHz under current constraints.

Extended parameters can lower GW echo frequency to around 100 Hz.

Abstract

Solid states of strange-cluster matter called strangeon matter can form strangeon stars that are highly compact. We show that strangeon matter and strangeon stars can be recast into dimensionless forms by a simple reparametrization and rescaling, through which we manage to maximally reduce the number of degrees of freedom. With this dimensionless scheme, we find that strangeon stars are generally compact enough to feature a photon sphere that is essential to foster gravitational-wave (GW) echoes. Rescaling the dimension back, we illustrate its implications on the expanded dimensional parameter space, and calculate the GW echo frequencies associated with strangeon stars, showing that the minimum echo frequency is $\sim 8$ kHz for empirical parameter space that satisfies the GW170817 constraint, and can reduce to $\mathcal O(100)$ Hertz at the extended limit.