Three-dimensional stability of magnetically confined mountains on accreting neutron stars

Abstract

We examine the hydromagnetic stability of magnetically confined mountains, which arise when material accumulates at the magnetic poles of an accreting neutron star. We extend a previous axisymmetric stability analysis by performing three-dimensional simulations using the ideal-magnetohydrodynamic (ideal-MHD) code zeus-mp, investigating the role played by boundary conditions, accreted mass, stellar curvature and (briefly) toroidal magnetic field strength. We find that axisymmetric equilibria are susceptible to the undular submode of the Parker instability but are not disrupted. The line-tying boundary condition at the stellar surface is crucial in stabilizing the mountain. The non-linear thre..