Compact Stars in F(R) Gravity Theory

F(R) gravity is a modified gravity theory, and its applications for the compact star have attracted attention in the last decades. We review the basics of the F(R) gravity theory and the modified Tolman-Oppenheimer-Volkoff (TOV) equation. Recent studies show that the model dependence of equation of state (EOS) and modification of gravity degenerate to each other, which suggests the mass-radius (M-R) relation of the compact star alone cannot completely determine the EOS of the inner matter. Moreover, the effects of a new scalar field predicted in F(R) gravity on both the internal and external structure of the compact star are illustrated in the benchmark R^2 model. Finally, We discuss the future directions for testing gravitational theories by observational measurements of the compact stars.