Astronomy Colloquium

Analyses of several recent experiments suggest that the symmetry energy of nuclear matter is now relatively well understood. The inferred symmetry energy is also very similar to that predicted by calculations of the properties of pure neutron matter. Since the behavior of the symmetry energy near the nuclear saturation density is closely coupled to the neutron star mass-radius relation, it is predicted that the radii of neutron stars with approximately 1.4 - 1.5 solar masses should lie in the range 11 to 12.5 km. This result is in substantial agreement with radii estimated from observations of quiescent neutron stars in globular clusters and photospheric radius expansion X-ray bursts. Neutron star radii together with the knowledge that the maximum neutron star mass exceeds 2 solar masses, as recent discoveries of massive neutron stars prove, can strongly constrain the properties of matter at densities several times greater than the nuclear saturation density.