A unified thermodynamic framework for coextensive dark matter admixed strange stars

TL;DR

This work develops a thermodynamically consistent, coextensive two-fluid framework for strange stars admixed with self-interacting bosonic dark matter. By introducing a fixed local volume fraction and a unified thermodynamic potential, it derives a single barotropic effective EOS that governs the combined system and solves the TOV equations to obtain mass–radius curves. The results show that dark matter admixture softens the EOS and reduces the maximum mass and radius, while lighter DM particles or stronger self-interactions stiffen the configuration, with quark matter stiffness playing a complementary role. The approach provides a direct link between dark-matter microphysics and observable stellar properties, offering a baseline for interpreting pulsar data and future tidal-deformability constraints in compact-star observations.

Abstract

We investigate the structural and physical properties of a strange star admixed with self-interacting bosonic dark matter. The total energy density is modelled as a weighted combination of quark matter and dark matter components regulated by a fixed local volume fraction. The quark component is described by a linear equation of state, while the dark matter follows a mean-field EOS with repulsive self-interactions. By combining these EOSs into a barotropic effective EOS derived from a unified thermodynamic potential, the two-fluid system is reformulated as a thermodynamically closed and mechanically equilibrated configuration. The construction preserves the dynamical distinction between the quark and dark sectors but treats them as a macroscopically unified mixture governed by a single hydrostatic equilibrium equation. This framework identifies the entirely coextensive limit of two-fluid models as a physically meaningful and thermodynamically closed configuration, providing a coherent macroscopic closure that links dark matter-strange matter microphysics to stellar observables. Using the effective EOS, we solve the governing Tolman-Oppenheimer-Volkoff (TOV) equations to obtain the mass-radius relationship by varying the model parameters. Our results reveal distinct modifications to the $M-R$ profiles, suggesting observable signatures that could offer insights into the impacts of dark matter in extreme astrophysical environments. We note that even a modest dark matter admixture softens the effective equation of state and shrinks the maximum mass limit. We discuss the relevance of our investigation in the context of recent observational data available for pulsars, such as XTE J1814-338, PSR J0348+0432, PSR J0740+6620 and PSRJ0952-0607.

Figures (18)

• Figure 1: Effective EOS of dark matter admixed strange stars calculated for various dark matter percentages and fixed values of $\lambda=\pi$ and $m_{\chi}=250~MeV$,$~a=0.4$, $\rho_0=400~ MeV~ fm^{-3}$.
• Figure 2: $M-R$ profiles of dark matter admixed strange stars calculated for various dark matter percentages and fixed values of $\lambda=\pi$ and $m_{\chi}=250~MeV$, $~a=0.4$, $\rho_0=400~ MeV~ fm^{-3}$.
• Figure 3: Effective EOS of dark matter admixed strange stars calculated for various dark matter particle masses and fixed values of $\lambda=\pi$ and dark matter percentage $=20\%$,$~a=0.4$, $\rho_0=400~ MeV~ fm^{-3}$.
• Figure 4: $M-R$ profiles of dark matter admixed strange stars calculated for various dark matter particle masses and fixed values of $\lambda=\pi$ and dark matter percentage $=20\%$, $~a=0.4$, $\rho_0=400~ MeV~ fm^{-3}$.
• Figure 5: Effective EOS of dark matter admixed strange stars calculated for various values of the self-coupling constant and fixed values of dark matter percentage $=10\%$ and $m_{\chi}=100~MeV$, $~a=0.4$, $\rho_0=400~ MeV~ fm^{-3}$.