Impact of the PSR J 0740 +6620 radius constraint on the properties of highdensity matter
Abstract
Xray pulse profile modeling of PSR J 0740 +6620 , the most massive known pulsar, with data from the NICER and XMMNewton 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 xray, radio and gravitationalwave observations of neutron stars. Our analysis mildly disfavors EoSs that support a disconnected hybrid star branch in the massradius 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_{⊙} . We also find that the conformal soundspeed bound is violated inside neutron star cores, which implies that the core matter is strongly interacting. The squared sound speed reaches a maximum of 0.7 5_{0.24}^{+0.25} c^{2} at 3.60_{1.89}^{+2.25} times nuclear saturation density at 90% credibility. Since all but the gravitationalwave observations prefer a relatively stiff EoS, PSR J 0740 +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.
 Publication:

Physical Review D
 Pub Date:
 September 2021
 DOI:
 10.1103/PhysRevD.104.063003
 arXiv:
 arXiv:2106.05313
 Bibcode:
 2021PhRvD.104f3003L
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology;
 Nuclear Theory
 EPrint:
 18 pages, 11 figures, data available at https://doi.org/10.5281/zenodo.5397808