The role of finite value of strange quark mass $(m_{s}\neq0)$ and baryon number density $(n)$ on the stability and maximum mass of strange stars

TL;DR

This paper investigates how finite strange quark mass and baryon density influence the structure, stability, and maximum mass of strange stars using a relativistic model with a density-dependent equation of state.

Contribution

It introduces a density-dependent MIT bag model with finite strange quark mass to better model phase transitions in strange stars.

Findings

Maximum mass for massless strange quarks is 2.01 solar masses.

Increasing strange quark mass slightly decreases maximum mass and radius.

Higher baryon density and quark mass influence phase transition conditions.

Abstract

This study describes the impact of non-zero value of strange quark mass $(m_{s})$ and number density of baryons $(n)$ on the structure, stability and maximum mass of strange stars. We derive an exact relativistic solution of the Einstein field equation using the Tolman-IV metric potential and modified MIT bag model EoS, $p_{r}=\frac{1}{3}(\rho-4B')$, where $B'$ is a function of bag constant $B$, $m_{s}$ and baryon number density $(n)$. Following CERN's findings, transition of phase from hadronic matter to Quark-Gluon Plasma (QGP) may occur at high densities in presence of favourable conditions. The standard MIT bag model, with a constant $B$, fails to explain such transition properly. Introducing a finite $m_{s}$ and Wood-Saxon parametrisation for $B$, dependent on baryon number density $(n)$, provides a more realistic EoS to address such phase transition. Both $m_{s}$ and $n$ constrain the EoS, making it softer as $m_{s}$ increases. Solutions to the TOV equations reveal that for massless strange quarks, maximum mass is 2.01 $M_{\odot}$ and corresponding radius is 10.96 Km when $n=0.66~fm^{-3}$. These values decrease to 1.99 $M_{\odot}$ and 1.96 $M_{\odot}$, with corresponding radii of 10.88 Km and 10.69 Km for $m_{s}=50$ and $100~MeV$ respectively having same $n$ value. It is interesting to note that a corelation exists between $n$ and $m_{s}$. The hadronic to quark matter transition occurs at higher values of $n$, when $m_{s}$ increases such as $n\geq0.484,~0.489$ and $0.51~fm^{-3}$ for $m_{s}=50$ and $100~MeV$ respectively. Beyond these values, the energy per baryon $(\mathcal{E_{B}})$ drops below $930.4~MeV$, indicating a complete transition to quark matter. For physical analysis, we have considered $n~(=0.578~fm^{-3})$ which lies in the stable region with $B(n)=70~MeV/fm^{3}$. The model provides a viable description of strange stars, satisfying all necessary physical requirements.