5 - Equilibrium models

Summary

Models in uniform rotation

Bulk properties

Neutron star models constructed with different proposed EOSs have strikingly different bulk properties, due to the large uncertainties in the equation of state above nuclear density. The overall relation between the equation of state and the structure of the star is easy to see: Because more compressible (soft) EOSs require a higher density to supply the same pressure, they yield stellar models with higher central density and smaller radius for a given mass than models based on less compressible (stiff) EOSs. Because less compact models have less gravitational binding energy for the same mass, models based on stiff EOSs can support more mass against gravitational collapse. Thus the maximum mass for a given EOS increases as the EOS becomes less compressible, attaining its largest value for models based on an incompressible EOS - for uniform-density models. Because the moment of inertia increases with increasing mass and (quadratically) with increasing radius, it shows the most rapid rate of increase with increasing stiffness of the EOS. On the other hand, because more compact stars can spin faster before reaching their maximum (Keplerian) rotation, the maximum spin for a fixed baryon mass increases as the compressibility increases.