Theoretical constraints on properties of low-mass neutron stars from EOS of inner crust matters

TL;DR

This paper theoretically investigates the properties of low-mass neutron stars using four EOS models of inner crust matter, identifying forbidden density and radius regions and analyzing how EOS softness affects star characteristics.

Contribution

It introduces constraints on low-mass neutron star properties based on EOS of inner crust matter, highlighting forbidden regions and dependencies of mass and radius on EOS softness.

Findings

Forbidden density region from 10^{12} to 10^{17} kg/m^3.

Forbidden radius region from 400 km to 2000 km.

Mass and radius depend on EOS softness at different densities.

Abstract

By employing four typical equation of states (EOSs) of the inner crust matters, the constraint on properties of low-mass neutron stars are theoretically investigated. Based on the well known fact that there is a big gap between the neutron stars and white dwarfs in the mass-radius sequence of compact stars, here we explicitly point out the forbidden region for the central density and stellar radius to form a compact stars, that is, there is no compact star in the nature having central density in the region from about $10^{12}~kg/m^3$ to $10^{17}~kg/m^3$, and there is also no compact star having a radius in the region from about 400 km to 2000 km. It is found that for a low-mass neutron star with central densities at subnuclear densities, the stellar mass is mainly determined by the softness of the EOS at the higher density region ($ > 10^{16}~\textrm{kg.m}^{-3}$) while the stellar radius is dependent on the softness of the EOS at lower density region ($ < 10^{16}~\textrm{kg.m}^{-3}$). For a stable neutron star with stellar mass near the minimum mass, the Keplerian period is several hundred millisecond, the moment of inertia is in an order of $10^{37} kg\cdot m^{2}$, and the surface gravitational redshift is in an order of $10^{-4}$.