The Shoenberg Effect in Relativistic Degenerate Electron Gas and Observational Evidences in Magnetars

The electron gas inside a neutron star is highly degenerate and relativistic. Due to the electron-electron magnetic interaction, the differential susceptibility can equal or exceed 1, which causes the magnetic system of the neutron star to become metastable or unstable. The Fermi liquid of nucleons under the crust can be in a metastable state, while the crust is unstable to the formation of layers of alternating magnetization. The change of the magnetic stress acting on adjacent domains can result in a series of shifts or fractures in the crust. The releasing of magnetic free energy and elastic energy in the crust can cause the bursts observed in magnetars. Simultaneously, a series of shifts or fractures in the deep crust which is closed to the Fermi liquid of nucleons can trigger the phase transition of the Fermi liquid of nucleons from a metastable state to a stable state. The released magnetic free energy in the Fermi liquid of nucleons corresponds to the giant flares observed in some magnetars.