2025ApJ...992...73J

The equation of state (EoS) of dense nuclear matter, particularly the symmetry energy that characterizes its isospin dependence, is of fundamental importance in neutron star (NS) physics and nuclear physics. Apart from the extensively used multimessenger astrophysics information, we introduce three new constraints to tighten the EoS at intermediate densities: (i) the absent direct Urca process in the 1.5 M_⊙ NS; (ii) the symmetry energy (coefficient) a_sym of ²⁰⁸Pb; (iii) the strong linear correlation between the slope parameter L of symmetry energy E_sym(ρ) at saturation density ρ₀ and E_sym(ρ₀) - a_sym. These constraints turn out to be highly effective for symmetry energy. As an alternative strategy, we employ the Bayesian statistical method with a multi-iteration procedure to ensure that the resulting posterior probability distribution is free of the initial prior distribution as far as possible. The most probable result of symmetry energy exhibits a soft behavior up to ∼2.5ρ₀, and then it rises rapidly as the density increases. On the one hand, our results allow one to explore a series of topics in NS physics. For instance, the radius and tidal deformability for a 1.4 M_⊙ NS are ${R}_{1.4}=12.4{6}_{-0.80}^{+0.22}\,{\rm{km}}$ and ${{\rm{\Lambda }}}_{1.4}=47{8}_{-183}^{+90}$. The vast majority of NSs are unlikely to contain deconfined quark matter in their cores. On the other hand, almost all the widely used nuclear many-body approaches fail to reproduce such a trend of symmetry energy, and hence our results serve as an important calibration for nuclear force and nuclear many-body approaches.