Collective electronic pulsation around giant nuclei in the Thomas-Fermi model

Abstract

Based on the Thomas-Fermi solution for compressed electron gas around a giant nucleus, $Z\approx 10^6$, we study electric pulsations of electron number-density, pressure and electric fields, which could be caused by an external perturbations acting on the nucleus or the electrons themselves. We numerically obtain the eigen-frequencies and eigen-functions for stationary pulsation modes that fulfill the boundary-value problem established by electron-number and energy-momentum conservation, equation of state, laws of thermodynamics, and Maxwell's equations, as well as physical boundary conditions. We choose a proton number of $Z=10^6$ and assume the nucleons in $β$-equilibrium at nuclear density. Similar systems with non-spherical geometry are hypothesized to exist in the lower crust of neutron stars, commonly referred to as \textit{pasta equation of state}. The lowest modes turn out to be heavily influenced by the relativistic plasma frequency induced by the positive charge background in the nucleus. We discuss the possibility to apply our results to dynamic nuclei using the spectral method and mention mechanisms that could stimulate such dynamics in the astrophysical context.