Impact of the newly revised gravitational redshift of x-ray burster GS 1826-24 on the equation of state of supradense neutron-rich matter
Wen-Jie Xie, Bao-An Li, Naibo Zhang
Abstract
Thanks to the recent advancement in producing rare isotopes and measuring their masses with unprecedented precision, the updated nuclear masses around the waiting-point nucleus $^{64}\mathrm{Ge}$ in the rapid-proton capture process have led to a significant revision of the surface gravitational redshift of the neutron star (NS) in GS 1826-24 by refitting its x-ray burst light curve [X. Zhou et al., Mass measurements show slowdown of rapid proton capture process at waiting-point nucleus $^{64}\mathrm{Ge}$, Nat. Phys. 19, 1091 (2023)] using Modules for Experiments in Stellar Astrophysics (MESA). The resulting NS compactness $\ensuremath{\xi}$ is between 0.183 and 0.259 at 95% confidence level, and its upper boundary is significantly smaller than the maximum $\ensuremath{\xi}$ previously known. Incorporating these new data within a comprehensive Bayesian statistical framework, we investigate its impact on the Equation of State (EOS) of supradense neutron-rich matter and the required spin frequency for GW190814's minor ${m}_{2}$ with mass $2.59\ifmmode\pm\else\textpm\fi{}0.05{M}_{\ensuremath{\bigodot}}$ to be a rotationally stable pulsar. We found that the EOS of high-density symmetric nuclear matter (SNM) has to be softened significantly while the symmetry energy at supersaturation densities stiffened compared to our prior knowledge from earlier analyses using data from both astrophysical observations and terrestrial nuclear experiments. In particular, the skewness ${J}_{0}$ characterizing the stiffness of high-density symmetric nuclear matter (SNM) decreases significantly, while the slope $L$, curvature ${K}_{\mathrm{sym}}$, and skewness ${J}_{\mathrm{sym}}$ of nuclear symmetry energy all increase appreciably compared to their fiducial values. We also found that the most probable spin rate for the ${m}_{2}$ to be a stable pulsar is very close to its mass-shedding limit once the revised redshift data from GS 1826-24 is considered, making the ${m}_{2}$ unlikely the most massive NS observed so far.