Relativistic figures of equilibrium in the Wald magnetosphere

Abstract

We consider a self-gravitating, rigidly rotating charged perfect fluid immersed in the Wald magnetosphere, constructed out of two linearly independent Killing vectors present in stationary and axially-symmetric spacetimes. We show that in non-vacuum spacetimes, Wald's solution can be compatible with the electric current associated with a rotating charged perfect fluid characterized by the vanishing electric conductivity. We prove that for rigidly rotating fluids with a constant energy density or described by the polytropic equation of state, the resulting equations expressing the conservation of the energy-momentum tensor can be integrated. Consequently, the system can be described by nearly standard Einstein-Euler equations known from the theory of general-relativistic rotating fluids, with modifications introduced in the Euler-Bernoulli equation. Numerical solutions of the Einstein-Euler equations are provided for these two cases by introducing suitable modifications in the pseudospectral code by Ansorg, Kleinw\"{a}chter, and Meinel.