2021/06/30 by Isaac Legred, Katerina Chatziioannou, Reed Essick +2 · 1 citation
Physics and Astronomy · #astro-ph.HE #gr-qc #nucl-th
paper · pdf · doi:10.1103/physrevd.104.063003
published as Phys. Rev. D 104, 063003 (2021) · 18 pages, 11 figures, data available at https://doi.org/10.5281/zenodo.5397808
arxiv created 2021/09/07 · arxiv updated 2021/09/09
X-ray pulse profile modeling of PSR J0740+6620, the most massive known pulsar, with data from the NICER and XMM-Newton observatories recently led to a measurement of its radius. We investigate this measurement's implications for the neutron star equation of state (EoS), employing a nonparametric EoS model based on Gaussian processes and combining information from other x-ray, radio and gravitational-wave observations of neutron stars. Our analysis mildly disfavors EoSs that support a disconnected hybrid star branch in the mass-radius relation, a proxy for strong phase transitions, with a Bayes factor of 6.9. For such EoSs, the transition mass from the hadronic to the hybrid branch is constrained to lie outside (1,2) M\odot. We also find that the conformal sound-speed bound is violated inside neutron star cores, which implies that the core matter is strongly interacting. The squared sound speed reaches a maximum of 0.75+0.25-0.24 c2 at 3.60+2.25-1.89 times nuclear saturation density at 90% credibility. Since all but the gravitational-wave observations prefer a relatively stiff EoS, PSR J0740+6620's central density is only 3.57+1.3-1.3 times nuclear saturation, limiting the density range probed by observations of cold, nonrotating neutron stars in β-equilibrium.