The properties of strange quark matter and evolution of strange quark stars

TL;DR

This paper addresses how strange quark stars (SQS) can evolve from proto-strange quark stars to cold, catalyzed SQS using a self-consistent thermodynamic framework based on a baryon-density-dependent quark-mass model. It derives thermodynamic quantities from a free-energy density $F(T,\{n_i\},\{m_i\})$ with density- and temperature-dependent masses $m_i(n_b,T)$, and enforces consistency with relations such as $P=-\Omega$ and $E=-P+\sum_i\mu_i n_i+TS$, verified by a test equation $P-n_b^2 d(F/n_b)/dn_b=0$. The study shows that as strange quarks emerge with deleptonization, the EOS softens and the maximum mass decreases from about $2.21\,M_\odot$ to $2.07\,M_\odot$, while radii shrink from roughly $14.1$ to $13.2$ km; the cold SQS predictions remain compatible with several massive pulsars, highlighting the model’s ability to explain compact stars that are challenging for standard neutron-star models. The framework and results offer a physically consistent approach to interpreting the evolution and observational signatures of SQM-based compact stars.

Abstract

In this work, we study the properties of strange quark matter and reveal the evolution process of strange quark stars employing a self consistent thermodynamic treatment. A comprehensive and reliable thermodynamic basis for the study of the dynamic evolution from proto-strange quark stars to stable strange stars at a zero temperature is provided. The relative abundance of particles, equation of state, temperature, and mass-radius relationship at each stage of the evolution of stars are discussed, where the cold strange quark star are consistent with the observational mass and radius of Hess J1731-347, PSR J1231-1411, PSR J0030+0451, PSR J0348+0432, and PSR J0740+6620, which could be difficult to be explained by the standard neutron star model. A schematic diagram is provided as well, illustrating the state of different stages along the evolution of stars at a fixed baryon-mass.

Figures (8)

• Figure 1: The stability window for the baryon density-dependent quark mass model.
• Figure 2: The relationship between the free energy per baryon, pressure and density at $T=50\ \mathrm{MeV}$, where $D^{1/ 2}=130.9\ \mathrm{MeV}$ and $C=0.69$.
• Figure 3: The relative particle fraction of the matter inside of strange quark stars as functions of baryon density at various snapshots of its evolution. The upper and lower panels are correspond to the neutrino-trapped and neutrino-transparent stage, respectively.
• Figure 4: The relationship between the pressure and energy density at different stages of evolution of SQS.
• Figure 5: The temperature as a function of baryon number density at different stages of evolution of SQS.