Study On Neutron Star Binding Energy And Its Universality

At present,the understanding of the equation of state of asymmetric nuclear matter(the matter in the neutron star’s core)several times the density of the saturated core is far from certain.But the EOS of highly dense nuclear matter is the key input for theoretical research on the structure and properties of neutron star.How to reduce the influence of the uncertainty of the EOS on the study of neutron stars? It is found that the universal relation between the property parameters of neutron star independent of the EOS can effectively reduce or eliminate the influence of the uncertainty of the EOS.The universality of neutron star binding energy has been studied for a long time.However,since the total binding energy of neutron star contains nuclear binding energy and gravitational binding energy,the gravitational binding energy can better reflect the mass distribution information of neutron star.Therefore,the gravitational binding energy is a better physical quantity than the compactness(M/R)of neutron star to express the universality relation of the parameters of neutron star properties.In this paper,we systematically study various universal relations based on the gravitational binding energy of neutron stars,including the universal relation between gravitational binding energy and compactness of neutron star,universal relation between moment of inertia and gravitational binding energy,universal relation between tidal deformation and gravitational binding energy,universal relation between gravitational binding energy and central density,etc.By comparing the existing universal relations of the moment of inertia with the compactness and the total binding energy,as well as the universal relations of the tidal deformation with the compactness and the moment of inertia,we find that the gravitational binding energy of neutron stars has a stronger universal relation with the moment of inertia and the tidal deformation.In the universal relation between gravitational binding energy and tidal deformation,the EOS of ordinary neutron star and the EOS of quark star will be separated into two curves.This can be used to distinguish ordinary neutron stars from quark stars.According to the universal relation between the gravitational binding energy and the moment of inertia(or tidal deformation),the third physical quantity can be estimated if any two physical quantities of the mass,moment of inertia(or tidal deformation)and the gravitational binding energy can be obtained from the observation.Finally,it is found that the above universality relation remains unchanged under the framework of Ei BI gravity theory.This suggests that we cannot use these universal relationships to distinguish between different theories of gravity.