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Constraining the Dense Matter Equation of State with New NICER Mass–Radius Measurements and New Chiral Effective Field Theory Inputs

2024; IOP Publishing; Volume: 971; Issue: 1 Linguagem: Inglês

10.3847/2041-8213/ad5f02

2041-8213

Nathan Rutherford, Melissa Mendes, Isak Svensson, A. Schwenk, Anna L. Watts, K. Hebeler, J. Keller, Chanda Prescod-Weinstein, Devarshi Choudhury, G. Raaijmakers, Tuomo Salmi, Patrick Timmerman, S. Vinciguerra, Sébastien Guillot, James M. Lattimer,

High-pressure geophysics and materials

Abstract Pulse profile modeling of X-ray data from the Neutron Star Interior Composition Explorer is now enabling precision inference of neutron star mass and radius. Combined with nuclear physics constraints from chiral effective field theory ( χ EFT), and masses and tidal deformabilities inferred from gravitational-wave detections of binary neutron star mergers, this has led to a steady improvement in our understanding of the dense matter equation of state (EOS). Here, we consider the impact of several new results: the radius measurement for the 1.42 M ⊙ pulsar PSR J0437−4715 presented by Choudhury et al., updates to the masses and radii of PSR J0740+6620 and PSR J0030+0451, and new χ EFT results for neutron star matter up to 1.5 times nuclear saturation density. Using two different high-density EOS extensions—a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS)—we find the radius of a 1.4 M ⊙ (2.0 M ⊙ ) neutron star to be constrained to the 95% credible ranges 12.28 − 0.76 + 0.50 km ( 12.33 − 1.34 + 0.70 km) for the PP model and 12.01 − 0.75 + 0.56 km ( 11.55 − 1.09 + 0.94 km) for the CS model. The maximum neutron star mass is predicted to be 2.15 − 0.16 + 0.14 M ⊙ and 2.08 − 0.16 + 0.28 M ⊙ for the PP and CS models, respectively. We explore the sensitivity of our results to different orders and different densities up to which χ EFT is used, and show how the astrophysical observations provide constraints for the pressure at intermediate densities. Moreover, we investigate the difference R 2.0 − R 1.4 of the radius of 2 M ⊙ and 1.4 M ⊙ neutron stars within our EOS inference.