Research On The Properties Of Low-mass Neutron Stars

The structure and properties of a neutron star are influenced by the equation of state(EOSs)of dense matter,but the central density of a low-mass neutron star does not exceed saturation nuclear density and the EOS in the inner crust has an crucial effect on the structure and stability of these stars.This paper is focused on theoretically investigating the properties of low-mass neutron stars by employing four typical EOSs of nuclear matter in the inner crust.By adopting TOV equation,we calculate the whole mass-radius relations of the compact stars from the white dwarf models up to the upper mass limit of neutron stars,where the EOSs of the inner crust are smoothly joined to both the EOSs of the uniform liquid inner core and the outer crust.It is shown that there is a rough forbidden region for the central density and stellar radius to form a compact star;that is,there is no compact star in nature having central density in the region from about 1012 kg/m3 to 1017 kg/m3,and there is also no compact star having a radius in the region from about 400 km to 2000 km.We can know simultaneously that for a stable neutron star near the minimum mass point,the stellar size(with radius>200 km)is much larger than that of normal neutron stars,and there is a compact“core" concentrated at about 95%of the stellar mass in the inner core with a radius of about 13 km and density higher than the neutron-drip point(pdrip = 4.3x1014kg/m3).This property totally differs from that of normal neutron stars and white dwarfs.Furthermore,the Keplerian period,the moment of inertia and the surface gravitational redshift of the star near the minimum-mass point are also investigated and is found to the relationships between these three quantities and the central density.These results will provide clues for the observation of low-mass neutron stars.