Electron exchange and polarization effects on electron captures and neutron emissions by nuclei in white dwarfs and neutron stars

Abstract

In dense stellar environments, nuclei may become unstable against electron captures and/or neutron emissions. These processes are of particular importance for determining the internal constitution of white-dwarf cores and neutron-star crusts. In this paper, the role of electron exchange and polarization effects is studied. In particular, the instability condition for the onset of electron captures and neutron emissions is extended so as to account for electron exchange and polarization. Moreover, general analytical expressions for the corresponding density and pressure are derived. The corrections to the electron-capture threshold in white-dwarf cores are found to be very small. Likewise, the neutron-drip density and pressure in the crusts of accreting and nonaccreting neutron stars are only slightly shifted. Depending on the nuclear mass model employed, electron polarization may change the composition of the crust of nonaccreting neutron stars. On the other hand, the current uncertainties in the masses of neutron-rich Kr and Sr isotopes are found to be more important than electron exchange and polarization effects.

arXiv comment15 pages, 4 figures

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• Massive white dwarfs in $f(R,L_m)$ gravity
• Experimental constraints on shallow heating in accreting neutron-star crusts
• Analytical determination of the structure and nuclear abundances of the outer crust of a cold nonaccreted neutron star
• Crust of accreting neutron stars within simplified reaction network
• Electrostatic energy of Coulomb crystals with polarized electron background
• Neutron transfer reactions in accreting neutron stars
• Accreting neutron stars from the nuclear energy-density functional theory. II. Equation of state and global properties
• Oscillations and tidal deformations of crystallized white dwarfs
• Pressure and chemical potentials in the inner crust of a cold neutron star within Hartree-Fock and extended Thomas-Fermi methods
• Layers of electron captures in the crust of accreting neutron stars