White dwarfs in regularized 4D Einstein-Gauss-Bonnet gravity

TL;DR

This paper investigates how 4D Einstein-Gauss-Bonnet gravity affects white dwarf structures, revealing deviations in mass-radius relations and stability features compared to general relativity, especially with larger Gauss-Bonnet coupling and anisotropic pressures.

Contribution

It introduces the analysis of white dwarf properties within 4D Einstein-Gauss-Bonnet gravity, incorporating realistic equations of state and anisotropic pressures, highlighting deviations from standard models.

Findings

Gauss-Bonnet term influences mass-radius relation and compactness.

Large $eta$ values lead to a second stable branch.

Impact of $ ext{α}$ is negligible for small values ($ extless 500 km^2$).

Abstract

White dwarfs (WDs), as the remnants of low to intermediate-mass stars, provide a unique opportunity to explore the interplay between quantum mechanical degeneracy pressure and gravitational forces under extreme conditions. In this study, we examine the structure and macroscopic properties of WDs within the framework of 4D Einstein-Gauss-Bonnet (4DEGB) gravity, a modified theory that incorporates higher-order curvature corrections through the Gauss-Bonnet coupling constant $\alpha$. Using the modified Tolman-Oppenheimer-Volkoff (TOV) equations tailored for 4DEGB gravity, we analyze the hydrostatic equilibrium of WDs modeled with a realistic equation of state (EoS). Our findings reveal that the inclusion of the Gauss-Bonnet (GB) term significantly influences the mass-radius ($M-R$) relation, allowing for deviations from the Chandrasekhar mass limit. In particular, we observe that such stars become more compact and slightly smaller with the increase of the parameter $\alpha$. For WDs with $\vert\alpha\vert \leq 500\, \rm km^2$, the impact of 4DEGB gravity appears to be negligible. However, a larger range for $\alpha$ allows for appreciable changes in the $M-R$ diagram, mainly in the high-central-density region. Furthermore, we explore the role of anisotropic pressures, quantified by the parameter $\beta$, on such systems and demonstrate their impact on stability and compactness. For sufficiently large values of $\vert\beta\vert$ keeping negative $\beta$ with a large and positive $\alpha$, there exists a second stable branch according to the classical stability criterion $dM/d\rho_c >0$. These results suggest that anisotropic WDs in 4DEGB gravity exhibit unique characteristics that distinguish them from their general relativistic counterparts, offering a novel testing ground for modified gravity theories in astrophysical settings.