Near-horizon description of extremal magnetised stationary black holes and Meissner effect

TL;DR

This paper explores the near-horizon geometries of extremal magnetised black holes, revealing a universal parameter and demonstrating magnetic field expulsion (Meissner effect) in these extreme conditions.

Contribution

It introduces a simplified characterization of extremal magnetised Kerr-Newman black holes using a single dimensionless parameter and demonstrates the Meissner effect in this context.

Findings

Near-horizon geometries are characterized by one effective parameter.

Magnetic fields are expelled from extremal black holes (Meissner effect).

Simplified models capture key properties of extremal magnetised black holes.

Abstract

After a brief summary of the basic properties of stationary spacetimes representing rotating, charged black holes in strong axisymmetric magnetic fields, we concentrate on extremal cases, for which the horizon surface gravity vanishes. We investigate their properties by constructing simpler spacetimes that exhibit their geometries near degenerate horizons. Starting from the symmetry arguments we find that the near-horizon geometries of extremal magnetised Kerr-Newman black holes can be characterised by just one dimensionless parameter: "effective Kerr-Newman mixing angle". Employing the near-horizon geometries we demonstrate the Meissner effect of magnetic field expulsion from extremal black holes.