The neutron skin thickness $\mathrm{\Delta }{r}_{\mathrm{np}}$ of heavy nuclei is essentially determined by the symmetry energy density slope $L\left(\rho \right)$ at ${\rho }_c=0.11{\mathrm{fm}}^{-3}\approx 2/3{\rho }_0$ (${\rho }_0$ is nuclear saturation density), roughly corresponding to the average density of finite nuclei. The PREX collaboration recently reported a model-independent extraction of $\mathrm{\Delta }{r}_{\mathrm{np}}^{208}=0.283\pm 0.071$ fm for the $\mathrm{\Delta }{r}_{\mathrm{np}}$ of ${}^{208}\mathrm{Pb}$, suggesting a rather stiff symmetry energy $E_{\mathrm{sym}}\left(\rho \right)$ with $L\left({\rho }_c\right)\ge 52$ MeV. We show that the $E_{\mathrm{sym}}\left(\rho \right)$ cannot be too stiff and $L\left({\rho }_c\right)\le 73$ MeV is necessary to be compatible with (1) the ground-state properties and giant monopole resonances of finite nuclei, (2) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (3) the largest neutron star (NS) mass reported so far for PSR $\mathrm{J0740}+6620$, (4) the NS tidal deformability extracted from gravitational wave signal GW170817, and (5) the mass-radius of PSR $\mathrm{J0030}+045$ measured simultaneously by NICER. This allows us to obtain $52\le L\left({\rho }_c\right)\le 73$ MeV and $0.212\le \mathrm{\Delta }{r}_{\mathrm{np}}^{208}\le 0.271$ fm and further $E_{\mathrm{sym}}\left({\rho }_0\right)=34.3\pm 1.7$ MeV, $L\left({\rho }_0\right)=83.1\pm 24.7$ MeV, and $E_{\mathrm{sym}}\left(2{\rho }_0\right)=62.8\pm 15.9$ MeV. A number of critical implications on nuclear physics and astrophysics are discussed.

• Received 15 February 2021
• Revised 9 February 2022
• Accepted 24 May 2022

DOI:https://doi.org/10.1103/PhysRevResearch.4.L022054

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society