Constraints on the dense matter equation of state from observations

Neutron stars are laboratories for dense matter physics. New observations of neutron stars from radio pulsars, X-ray binaries, quasi-periodic oscillators, X-ray bursters and thermally-emitting isolated neutron stars are setting bounds to masses, radii, rotation rates, radiation radii, redshifts, moments of inertia, temperatures and ages. Radio pulsar data suggest a broader range of masses than expected. Radiation radii measurements from isolated neutron stars and from X-ray sources in globular clusters are also becoming available. But the most precise radius measurement may come from possible moment of inertia measurement from relativistic binary pulsars. The largest pulsar rotation rates set upper bounds to the ratio R³/M, and quasi-periodic oscillations, if associated with the innermost stable orbit, set upper limits to both M and R. Observations of cooling neutron stars up to a million years old shed light on their internal compositions, including their superfluid properties, by constraining the neutrino emission rates.