Black holes with current loops revisited

Abstract

The electromagnetic field around a Kerr black hole inside a current loop is sometimes used as the basis of a toy model for discussing the properties of particle orbits near astrophysical black holes. The motivation for the present paper is to correct the published solution to Maxwell's equations with a charged current loop. Dipole approximations and closed-form expressions in the extreme Kerr limit are also presented. Using the corrected solution, it turns out that imposing a vanishing electromotive force produces a loop with a potential which is finite everywhere outside the black hole. Ring solutions can be combined into solutions with multiple rings or current discs.