Force-free magnetosphere attractors for near-horizon extreme and near-extreme limits of Kerr black hole

TL;DR

This paper introduces a new perturbative approach to constructing force-free magnetospheres around highly spinning Kerr black holes, utilizing attractor solutions in near-horizon limits to model astrophysical jets.

Contribution

It develops a universal perturbative framework based on attractor solutions in NHEK and near-NHEK limits for modeling magnetospheres around extreme Kerr black holes.

Findings

Identified a universal attractor solution in the NHEK limit for force-free magnetospheres.

Constructed magnetically dominated magnetospheres via second-order perturbation theory.

Discovered a novel attractor in the near-NHEK regime applicable to near-extreme Kerr black holes.

Abstract

We propose a new approach to find magnetically-dominated force-free magnetospheres around highly spinning black holes, relevant for models of astrophysical jets. Employing the near-horizon extreme Kerr (NHEK) limit of the Kerr black hole, any stationary, axisymmetric and regular force-free magnetosphere reduces to the same attractor solution in the NHEK limit with null electromagnetic field strength. We use this attractor solution as the universal starting point for perturbing away from the NHEK region in the extreme Kerr spacetime. We demonstrate that by going to second order in perturbation theory, it is possible to find magnetically dominated magnetospheres around the extreme Kerr black hole. Furthermore, we consider the near-horizon near-extreme Kerr (near-NHEK) limit that provides access to a different regime of highly spinning black holes. Also in this case we find a novel force-free attractor, which can be used as the universal starting point for a perturbative construction of force-free magnetospheres. Finally, we discuss the relation between the NHEK and near-NHEK attractors.