Dark-Energy Anisotropic Compact Configurations in 4D Einstein-Gauss-Bonnet Gravity: From Structure to Observational Viability

TL;DR

This paper investigates anisotropic compact stars in 4D Einstein-Gauss-Bonnet gravity with modified Chaplygin gas, analyzing their structure, stability, and observational viability, revealing conditions for ultra-compact configurations exceeding 2 solar masses.

Contribution

It introduces a comprehensive numerical analysis of anisotropic dark-energy stars in 4DEGB gravity, exploring parameter effects on stability and observational constraints, which is novel in this context.

Findings

Positive Gauss-Bonnet coupling and anisotropy increase maximum mass and radius.

Configurations can exceed 2 solar masses while remaining stable and causal.

Certain parameter regions align with astrophysical observations like NICER and gravitational wave data.

Abstract

We address the equilibrium configurations and stability properties of anisotropic compact stars whose interior is described by a modified Chaplygin gas (MCG) equation of state in the framework of the regularized four-dimensional Einstein-Gauss-Bonnet (4DEGB) theory. Applying a quasi-local prescription for the pressure anisotropy, we derive the modified Tolman-Oppenheimer-Volkoff (TOV) equations and integrate them numerically over a large parameter space in the Gauss-Bonnet coupling $\alpha$ and the degree of anisotropy $\beta$. We provide mass-radius sequences, mass-compactness, energy density, and pressure profiles, and perform a full stability analysis based on the turning-point criterion, the radial adiabatic index $\gamma_r$, and the radial and transverse sound speeds $v_r^2$ and $v_t^2$. Our results show that positive $\alpha$ and positive anisotropy $(\beta > 0)$ systematically increase the maximum mass and radius, enabling then configurations that exceed $2\,M_\odot$ while still obeying causality and the modified Buchdahl bound in 4DEGB gravity. A comparison with the latest astrophysical constraints (NICER, GW170817, GW190814, and massive-pulsar measurements) identifies regions of the $(\alpha,\beta)$ parameter space that are observationally allowable. In conclusion, anisotropic dark-energy stars in 4DEGB gravity provide viable, observationally testable ultra-compact alternatives to normal neutron stars and black holes, and also potentially open rich avenues for further multi-messenger searches for higher-curvature effects.