Structure of neutron star in Rastall gravity

Abstract

Using the AV18 equation of state, we numerically calculate the structure of a neutron star in Rastall gravity. The results show that the parameter $\lambda$ originated from Rastall gravity has a great effect on the mass and the radius of a neutron star. When $\lambda =1$, the Rastall equations of motion can be reduced to those in the general relativity. In terms of the stability condition for the Rastall equation of hydrostatic equilibrium, $\lambda$ can be divided into two regions: $[1,+\infty )$ and $(-\infty ,-1)$. In these two regions, the maximum mass and radius of a star increase with $\lambda$ increasing. As $\lambda$ is large enough in the range of $\lambda \geqslant 1$, the maximum mass and radius tend towards 7.43$M_{\odot}$ and 35.65 km. While $\lambda$ is small enough in the range of $\lambda <-1$, the maximum mass and radius are approximately 7.45$M_{\odot}$ and 35.55 km. It is interesting that the upper maximum mass is 9.76$M_{\odot}$ when $\lambda$ tends to −1 and the lower maximum mass is 1.65$M_{\odot}$ as $\lambda =1$. Furthermore, when $\lambda \approx 1.16$, there exist two neutron stars with the equal maximum mass, 1.92$M_{\odot}$, and different radii, 13.28 km and 22.85 km.