Loss of stability of low-mass stars under neutronization

Results of numerical computations of the final evolution phase and of the loss of the mechanical stability in iron nuclei with masses 1.21 (Sum mass), 1.4 (Sum mass) and 1.7 (Sum mass) are given. The emission and electron-positron gas thermodynamics was calculated using exact formulae. The chemical composition was determined at T > 3.99 deg K from the condition of statistical equilibrium over nuclei. Consecutive was taken of the kinetics of β-processes. Hydrodynamics equation were solved in the approximation of the profiled density according to the polytropic law with n=3. Pronounced mechanical stability loss and transfer into the hydrodynamic compression phase are observed in models with 1.7 (Sum mass) and 1.4 (Sum mass) masses. It is impossible to point out such a moment in the 1.21 (Sum mass) model; the star evolution with the characteristic time of β-processes gradually passes into the hydrodynamic phase of collapse. The thermodynamically non-equilibrium character of β-processes, which leads to the entropy growth in the stars central regions, plays an important role in all models and in the model with M=1.21 (Sum mass) in particular. URCA-neutrinos give the main contribution to the rate of energy losses in all models. The possibility of the neutron star production with small masses M < 1 (Sum mass) is discussed