Constraint on the equation of state of strange quark star: Perturbative QCD along with a density-dependent bag constant

TL;DR

This paper develops a density-dependent perturbative QCD model with a variable bag constant to better describe strange quark stars, successfully explaining observed massive compact objects and satisfying multiple astrophysical constraints.

Contribution

It introduces a novel density-dependent bag constant in perturbative QCD to improve the modeling of strange quark star equations of state, enabling explanations of massive stars beyond 2 solar masses.

Findings

Density-dependent bag constant significantly alters the EOS.

Massive SQSs exceeding 2 solar masses are achievable.

EOS consistent with gravitational wave and stability constraints.

Abstract

This study investigates the structural properties of strange quark stars (SQS) using a Quantum Chromodynamics (QCD) perturbative model combined with the latest Particle Data Group dataset. Given the energy scale present in compact stars, QCD perturbation theory alone may not fully explain their structure. To account for non-perturbative contributions, we incorporate a density-dependent effective bag parameter, $B$, and derive the equation of state (EOS) for strange quark matter (SQM). We start by demonstrating the limitations of EOSs with a constant $B$ in describing massive objects with $ M_{TOV}> 2M_{\odot} $. Subsequently, we show that considering $B$ as a density-dependent function significantly changes the results. Our definition of $B$ includes two parameters determined by both theoretical and observational constraints. We demonstrate that incorporating a density-dependent $B$ into the perturbative EOS can yield SQSs with masses exceeding $2M_{\odot}$, while complying with gravitational wave constraints such as tidal deformability, and thermodynamic considerations, including stability conditions and speed of sound behavior. Specifically, we show that massive compact objects like PSR J0952-0607, PSR J2215+5135, PSR J0740+6620, and the secondary mass of GW190814 can be SQSs. Additionally, we compare our EOS with the EOS of the authors who use a generalized polytropic form with adjustable parameters and obtain an interesting result.