Neutron star masses and radii

This contribution describes constraints on neutron star masses and radii, and the underlying dense matter equation of state, from general relativity, causality, and the observed lower limit to the neutron star maximum mass. Further constraints can be achieved from theoretical studies of neutron matter, including a lower bound on its energy from the unitary gas, and experimental studies of nuclei. These constraints are compared to observational X-ray measurements of photospheric radius expansion bursts and quiescent low-mass binaries. The recent observation of gravitational waves from the binary neutron star merger GW170817 has provided even more powerful constraints. Upcoming measurements from phase-resolved spectroscopy of pulsars and the moment of inertia of PSR J0737-3039A are also discussed.