Implications of latest NICER data for the neutron star equation of state

As an update to our previously performed Bayesian inference analyses of the neutron star matter equation-of-state and related quantities, the additional impact of the recently published NICER data of PSR J0437-4751 is examined. Including the mass and radius distributions of this pulsar in our database results in modest shifts from previously inferred median posterior values of radii R and central densities nc for representative 1.4M⊙ and 2.1M⊙ neutron stars: radii are reduced by about 0.2–0.3 km to values of R1.4=12.1±0.5 km and R2.1=11.9−0.6+0.5 km (at the 68% level), and central densities increase slightly to values of nc(1.4M⊙)/n0=2.8±0.3 and nc(2.1M⊙)/n0=3.8−0.7+0.6 (in units of equilibrium nuclear matter density, n0=0.16 fm−3)—i.e., they still fall below five times nuclear saturation density at the 68% level. As a further significant result, the evidence established by analyzing Bayes factors for a trace anomaly measure, Δ=1/3−P/ϵ<0, inside heavy neutron stars is raised to . Published by the American Physical Society 2025