Strange quark stars: the role of excluded volume effects

TL;DR

This paper investigates how excluded volume effects influence the properties and stability of cold strange quark stars using an enhanced quark-mass density-dependent model, showing significant impacts on mass, radius, and astrophysical compatibility.

Contribution

It introduces an improved model incorporating excluded volume effects and analyzes their impact on quark star stability, mass-radius relations, and astrophysical constraints.

Findings

Excluded volume effects do not alter the stability window at zero pressure.

Mass-radius curves shift towards larger radii with increased excluded volume effects.

Models become compatible with recent astrophysical observations, including low-mass compact objects.

Abstract

We study cold strange quark stars employing an enhanced version of the quark-mass density-dependent model which incorporates excluded volume effects to address non-perturbative QCD repulsive interactions. We provide a comparative analysis of our mass formula parametrization with previous models from the literature. We identify the regions within the parameter space where three-flavor quark matter is more stable than the most tightly bound atomic nucleus (stability window). Specifically, we show that excluded volume effects do not change the Gibbs free energy per baryon at zero pressure, rendering the stability window unaffected. The curves of pressure versus energy density exhibit various shapes -- convex upward, concave downward, or nearly linear -- depending on the mass parametrization. This behavior results in different patterns of increase, decrease, or constancy in the speed of sound as a function of baryon number density. We analyze the mass-radius relationship of strange quark stars, revealing a significant increase in maximum gravitational mass and a shift in the curves towards larger radii as the excluded volume effect intensifies. Excluded volume effects render our models compatible with all modern astrophysical constraints, including the properties of the recently observed low-mass compact object HESSJ1731.