# Implications of the mass $M=2.17^{+0.11}_{-0.10}$M$_\odot$ of PSR~J0740+6620 on the Equation of State of Super-Dense Neutron-Rich Nuclear Matter

## TL;DR

This paper explores how the recent measurement of PSR J0740+6620's mass influences the understanding of the nuclear matter equation of state, impacting model constraints and neutron star properties.

## Contribution

It updates constraints on the nuclear matter EOS using the new neutron star mass, notably raising the lower limit of the skewness parameter and the symmetry energy at high densities.

## Key findings

- Lower limit of skewness J_0 increased from -220 MeV to -150 MeV.
- Minimum proton fraction in neutron stars rises from 0 to 5%.
- Some existing EOS models struggle to match the new mass and tidal deformability constraints.

## Abstract

We study implications of the very recently reported mass $M=2.17^{+0.11}_{-0.10}$M$_\odot$ of PSR~J0740+6620 on the Equation of State (EOS) of super-dense neutron-rich nuclear matter with respect to existing constraints on the EOS based on the mass $M=2.01\pm 0.04$M$_\odot$ of PSR~J0348+0432, the maximum tidal deformability of GW170817 and earlier results of various terrestrial nuclear laboratory experiments. The lower limit of the skewness $J_0$ measuring the stiffness of super-dense isospin-symmetric nuclear matter is raised raised from about -220 MeV to -150 MeV, reducing significantly its current uncertainty range. The lower bound of the high-density symmetry energy also increases appreciably leading to a rise of the minimum proton fraction in neutron stars at $\beta$-equilibrium from about 0 to 5\% around three times the saturation density of nuclear matter. The difficulties for some of the most widely used and previously well tested model EOSs to predict simultaneously both a maximum mass higher than 2.17 M$_\odot$ and a pressure consistent with that extracted from GW170817 present some interesting new challenges for nuclear theories.