Massive white dwarfs in $f(R,L_m)$ gravity

TL;DR

This paper explores how a modified gravity theory, $f(R,L_m)$ gravity, affects the structure and maximum mass of white dwarfs, showing it can explain super-Chandrasekhar white dwarfs with masses exceeding traditional limits.

Contribution

First application of $f(R,L_m)$ gravity to white dwarfs, demonstrating its potential to produce super-Chandrasekhar masses and recover GR results for larger stars.

Findings

Maximum white dwarf masses exceed Chandrasekhar limit

Theory accommodates super-Chandrasekhar white dwarfs with various compositions

GR results are recovered for stars larger than 3000 km

Abstract

In this work, we investigate the equilibrium configurations of massive white dwarfs (MWD) in the context of modified gravity, namely $f(R,L_m)$ gravity, where $R$ stands for the Ricci scalar and $L_m$ is the Lagrangian matter density. We focused on the specific case $f(R,L_m) = R/2 + L_m + \sigma RL_m$, i.e., we have considered a non-minimal coupling between the gravity field and the matter field, with $\sigma$ being the coupling constant. For the first time, the theory is applied to white dwarfs, in particular to study massive white dwarfs, which is a topic of great interest in the last years. The equilibrium configurations predict maximum masses which are above the Chandrasekhar mass limit. The most important effect of the theory is to increase significantly the mass for stars with radius < 2000 km. We found that the theory can accommodate the super-Chandrasekhar white dwarfs for different star compositions. Apart from this, the theory recovers the General Relativity results for stars with radii larger than 3000 km, independent of the value of $\sigma$.