The Equation of State of Neutron-Rich Matter and Neutron Star Observations

The equation of state of neutron-rich matter plays a key role in the properties of neutron stars and is connected with the properties of heavy neutron-rich nuclei. The nuclear symmetry energy, the energy cost of creating an isospin asymmetry is of particular interest. Neutron star radius measurements, nuclear data, quantum Monte Carlo, and chiral effective theory are collectively creating a consistent picture of the equation of state of neutron-rich matter. These results suggest that the density derivative of the nuclear symmetry energy, L, is relatively small. I will describe the neutron star radius measurements and how Bayesian techniques are helping make the connection to the equation of state and the value of L. I will also show how these statistical methods are helping us probe systematic uncertainties. Finally, I will summarize other constraints on the symmetry energy and show that they generally agree with the information which we have from neutron stars.