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

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 + σ RL m , i.e., we have considered a non-minimal coupling between the gravity field and the matter field, with σ 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 σ . IntroductionRecently, the possibility of some white dwarfs (WD) surpassing the Chandrasekhar mass limit was raised [1-6]. The possible progenitor of such massive stars (M > 2M ) are being termed super-Chandrasekhar white dwarfs. In this context, plenty of works have been done to model these very massive white dwarfs (MWD). The properties of MWDs have been studied in different contexts: rotation [7-10]; high electric and magnetic fields [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]; temperature [27,28] and modified gravity [29][30][31][32][33][34][35][36][37][38][39][40]. It has been shown that general relativistic effects are essential for massive white dwarfs