An exact rotating black-hole solution in pure Einstein-Maxwell theory admits a cosmological horizon whose radius is set by the electromagnetic field strength alone.
Ergoregions in Magnetised Black Hole Spacetimes
7 Pith papers cite this work. Polarity classification is still indexing.
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Pith papers citing it
abstract
The spacetimes obtained by Ernst's procedure for appending an external magnetic field $B$ to a seed Kerr-Newman black hole are commonly believed to be asymptotic to the static Melvin solution. We show that this is not in general true. Unless the electric charge of the black hole satisfies $Q= jB(1+ 1/4 j^2 B^4)$, where $j$ is the angular momentum of the original seed solution, an ergoregion extends all the way from the black hole horizon to infinity. We give a self-contained account of the solution-generating procedure, including including explicit formulae for the metric and the vector potential. In the case when $Q= jB(1+ 1/4 j^2 B^4)$, we show that there is an arbitrariness in the choice of asymptotically timelike Killing field $K_\Omega= \partial/\partial t+ \Omega \partial/\partial \phi$, because there is no canonical choice of $\Omega$. For one choice, $\Omega=\Omega_s$, the metric is asymptotically static, and there is an ergoregion confined to the neighbourhood of the horizon. On the other hand, by choosing $\Omega=\Omega_H$, so that $K_{\Omega_H}$ is co-rotating with the horizon, then for sufficiently large $B$ numerical studies indicate there is no ergoregion at all. For smaller values, in a range $B_-<B<B_+$, there is a toroidal ergoregion outside and disjoint from the horizon. If $B\le B_-$ this ergoregion expands all the way to infinity in a cylindrical region near to the rotation axis. For black holes whose size is small compared to the Melvin radius 2/B, we recover Wald's result that it is energetically favourable for the hole to acquire a charge $2jB$.
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Unique quasi-topological theories with first-order equations are found for Taub-NUT, NHEK, swirling and related 4D symmetric metrics, enabling closed-form solutions and regular black holes from high-order curvature corrections.
A trapped-surface criterion, derived under null convergence and generic conditions, rules out superextremal Reissner-Nordström, Kerr-Newman, and related final states in overcharging thought experiments without using asymptotic charges.
A new Ricci-flat rotating metric is obtained by demagnetizing the KBR solution, yielding a deformed Kerr geometry with non-flat asymptotics for which black hole thermodynamics is established.
Magnetic fields lower the scalarization threshold for electromagnetic and gravitational Chern-Simons couplings but produce opposite trends on the two Gauss-Bonnet branches, with nonlinear terms converting exponential growth into bounded oscillations.
Solar-system tests constrain the spindle deformation parameter to |B| ≲ 10^{-24}--10^{-23} cm^{-1} from perihelion data and |B| ≲ 10^{-21} cm^{-1} from light-travel time.
The static Reissner-Nordström black hole embedded in Bertotti-Robinson (AdS₂ × S²) is supersymmetric in N=2 D=4 supergravity, saturates the BPS bound, and yields mass and thermodynamic relations with a cosmological-constant generalization.
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New Rotating Black Hole in Electromagnetic Fields: Cosmological Horizon without Cosmological Constant
An exact rotating black-hole solution in pure Einstein-Maxwell theory admits a cosmological horizon whose radius is set by the electromagnetic field strength alone.
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Quasi-topological gravity for 4-dimensional Taub-NUT, near-horizon extreme Kerr, and swirling symmetries
Unique quasi-topological theories with first-order equations are found for Taub-NUT, NHEK, swirling and related 4D symmetric metrics, enabling closed-form solutions and regular black holes from high-order curvature corrections.
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Trapped Surface as a Cosmic Censor
A trapped-surface criterion, derived under null convergence and generic conditions, rules out superextremal Reissner-Nordström, Kerr-Newman, and related final states in overcharging thought experiments without using asymptotic charges.
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Demagnetizing KBR and New Ricci-flat Rotating Metric
A new Ricci-flat rotating metric is obtained by demagnetizing the KBR solution, yielding a deformed Kerr geometry with non-flat asymptotics for which black hole thermodynamics is established.
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Scalarizations of magnetized Reissner-Nordstr\"om black holes induced by parity-violating and parity-preserving interactions
Magnetic fields lower the scalarization threshold for electromagnetic and gravitational Chern-Simons couplings but produce opposite trends on the two Gauss-Bonnet branches, with nonlinear terms converting exponential growth into bounded oscillations.
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Solar-System Bounds on Ricci-flat Spindle Deformations of Schwarzschild
Solar-system tests constrain the spindle deformation parameter to |B| ≲ 10^{-24}--10^{-23} cm^{-1} from perihelion data and |B| ≲ 10^{-21} cm^{-1} from light-travel time.
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Supersymmetry of the static Reissner-Nordstr\"om black hole in Bertotti-Robinson ($\mathrm{AdS}_2 \times \mathbb{S}^2$)
The static Reissner-Nordström black hole embedded in Bertotti-Robinson (AdS₂ × S²) is supersymmetric in N=2 D=4 supergravity, saturates the BPS bound, and yields mass and thermodynamic relations with a cosmological-constant generalization.