Magnetic collapse of a neutron gas: Can magnetars indeed be formed

Abstract

A relativistic degenerate neutron gas in equilibrium with a background of electrons and protons in a magnetic field exerts its pressure anisotropically, having a smaller value perpendicular than along the magnetic field. For critical fields the magnetic pressure may produce the vanishing of the equatorial pressure of the neutron gas. Taking it as a model for neutron stars, the outcome could be a transverse collapse of the star. This fixes a limit to the fields to be observable in stable neutron star pulsars as a function of their density. The final structure left over after the implosion might be a mixed phase of nucleons and meson condensate, a strange star, or a highly distorted black hole or black "cigar", but no any magnetar, if viewed as a super strongly magnetized neutron star. However, we do not exclude the possibility of a supersotrong magnetic fields arising in supernova explosions which lead directly to strange stars. In other words, if any magnetars exist, they cannot be neutron stars.

Comments: 15 pages, 3 figures. European Physical Journal C in press