Implications of Matter--Curvature Coupled Gravity on Chandrasekhar Mass Limit of White Dwarfs

Abstract

We investigate white dwarfs in the framework of f(R,Lm) and f(R,Lm,T) gravity to explore the Chandrasekhar limit. We have considered two functional forms of f(R,Lm) and one functional form of f(R,Lm,T) gravity. Considering the matter Lagrangian Lm=p , we calculate modified TOV equations for each of the forms. By employing the fully degenerate electron gas equation of state in the modified ToV equations, we derive the mass-radius relation for each functional form of both f(R,Lm) and f(R,Lm,T) gravity. Our models imply modifications in the Chandrasekhar mass limit that deviate significantly from the GR and the Newtonian cases. In the f(R,Lm,T) gravity, the new mass limit of the white dwarf can reach up to 1.537M while in f(R,Lm,T) with the quadratic extension can reach up to 1.52M and with square-root exponential model extension up to 2.08M. Further, we analyze the static stability criterion, the gravitational redshift, and the adiabatic indices. For the power-law form of f(R,Lm) and the nonlinear form of f(R,Lm,T) gravity, significant variations are observed at higher densities rho_c>1010gcm^-3, while substantial changes are noted at much lower central densities in the case of square-root exponential model form of f(R,Lm) gravity. The higher-density configurations should be regarded as formal equilibrium solutions within the adopted Chandrasekhar EoS and not as fully realistic stable C-O WDs, since additional high-density microphysics has not been included. We also calculate compactness and gravitational redshift, which are much lower than those of NS and BH. The configuration satisfies the adiabatic stability criterion, which shows that all considered models yield Gamma > 4/3 throughout the interiors of WDs. Overall, our models provide a viable framework for the existence of superChandrasekhar mass limit, extending beyond the classical predictions in the Newtonian and/or GR cases.