Structure Of The Neutron Star In Rastall Gravity

Neutron stars are some of the densest manifestations of massive objects in the universe that formed after supernova explosion.There are many characteristics for neutron stars,such as high density and strong magnetic field,strong gravitational field making them ideal astrophysical laboratories for testing theories of gravity.In 1972,P.Rastall proposed a modified theory of gravity,called Rastall gravity.This theory proposed that the energy was not conserved in curved space-time,and the covariant derivative of the energy-momentum tensor was proportional to the covariant derivative of the curvature scalar.The equations of motion in Rastall gravity recovered the standard field equations in the general theory of relativity in the case of the Rastall parameter with a suitable value or in the flat space-time.Based on the hydrostatic equilibrium equation of Rastall gravity theory,this paper discussed the structure of neutron stars using two kinds of equations of state AV18 and BSk19,respectively.In chapter 1,we gave an overview of neutron stars,including their formation,properties and etc.In Chapter 2,we reviewed the hydrostatic equilibrium equation(TOV equation)in the framework of general relativity,and discussed the structure of neutron stars in general relativity using a polytropic equation of state.In Chapter 3,we expatiated the theory of Rastall gravity and discussed the possible Lagrangians for Rastall gravity.In Chapter 4,we firstly deduced the star structure equation in Rastall gravity(RTOV).Secondly,using the AV18 equation of state,we numerically calculated the neutron star structure in Rastall gravitational theory.The results showed that the parameter ? originated from the Rastall gravity has a great effect on the mass and the radius of a neutron star.Whether ??[1,+?)or ??(-?,-1),the maximum mass and radius of a star increase with ? increasing.As ? is large enough in the range of ??1,the maximum mass tends to 7.43M?.While ? is small enough in the range of ?<-1,the maximum mass is approximately 7.45M?.It is interesting that the upper maximum mass is 9.76M?when ? tends to-1 and the lower maximum mass is1.65M?as ?=1.Furthermore,when ??1.16,there exist two neutron stars with the equal maximum mass,1.92M?,and different radii,13.28 km and 22.85 km.Finally,using the BSk19 equation of state,we calculated the neutron star structure in Rastall gravitational theory.The numerical results obtained are the same as the relationship between the Rastall neutron star structure and the Rastall gravitational parameter ?with the AV18 equation of state.In Chapter 5,we summarized the work in this paper,and looked forward to future research.