The interplay of astrophysics and nuclear physics in determining the properties of neutron stars

Neutron star properties depend on both nuclear physics and astrophysical processes, and thus observations of neutron stars offer constraints on both large-scale astrophysics and the behavior of cold, dense matter. In this study, we use astronomical data to jointly infer the universal equation of state of dense matter along with two distinct astrophysical populations: Galactic neutron stars observed electromagnetically and merging neutron stars in binaries observed with gravitational waves. We place constraints on neutron star properties and quantify the extent to which they are attributable to macrophysics or microphysics, and confirm previous results indicating that the Galactic and merging neutron stars have distinct mass distributions. We find the inferred maximum mass of both Galactic neutron stars and neutron stars in merging binaries are consistent with the maximum mass of nonrotating neutron stars set by nuclear physics. We provide constraints on the radius of a 1.4 solar mass neutron star that are ∼20% tighter than previous results using an identical equation of state model. We conclude there is currently no evidence that astrophysical processes cannot produce neutron stars up to the maximum value imposed by nuclear physics.