What neutron star collisions tell us about nuclear matter

Neutron stars are cosmic laboratories for nuclear physics. By combining gravitational wave detections from colliding neutron stars (GW170817) with X-ray timing measurements from NICER and pulsar mass observations, researchers constrained the equation of state—how pressure relates to density inside these objects. Their Bayesian analysis shows astrophysics data tightens the allowed pressure range so much that theoretical uncertainties from nuclear physics barely matter. The result: the nuclear symmetry energy parameter is pinned to 43–57 MeV, and matter stiffens significantly at densities three times that of atomic nuclei.