A Convergence on an Understanding of the Dense Matter Equation of State
Determining the equation of state of neutron star matter has been a
long-sought goal. Recently, there has been a remarkable convergence
in our understanding of dense matter from several directions: multiple
nuclear experiments, theoretical neutron matter studies, pulsar mass
determinations, and estimates of neutron star masses and radii from
X-ray sources. The key parameters are related to the symmetry energy
of matter near the nuclear saturation density, which is closely
related to the neutron star mass-radius relation. Observations
indicate that the maximum neutron star mass is in excess of 2 solar
masses, and, together with nuclear experimental and theoretical
studies, restrict the radii of neutron stars with approximately 1.4 -
1.5 solar masses to lie in the range 11 to 12.5 km. In addition, the
rapid cooling recently found for the neutron star in the Cassiopeia
supernova remnant indicates that both neutron superfluidity and proton
superconductivity exist in its interior, and tightly constrain their
respective critical temperatures.