Electromagnetic duality degeneracy in dynamical black hole mergers

TL;DR

This paper demonstrates electromagnetic duality symmetry in dynamical black hole mergers through numerical simulations, revealing a degeneracy in gravitational observables and a polarization rotation in emitted radiation.

Contribution

First fully nonlinear realization of electromagnetic duality in dynamical strong-gravity regimes via numerical relativity simulations of charged black hole mergers.

Findings

Dual configurations show identical spacetime dynamics.

Electromagnetic radiation polarization rotates with duality angle.

Electromagnetic duality acts as an organizing principle for solutions.

Abstract

Electromagnetic duality is a symmetry of the source-free Einstein-Maxwell equations that rotates electric and magnetic fields while leaving the stress-energy tensor invariant. We present the first fully nonlinear realization of this symmetry in dynamical strong-gravity regimes by performing numerical relativity simulations of charged black hole mergers across a continuous duality family. Starting from electrically charged binaries, we generate dyonic and magnetically charged configurations via duality rotations and evolve them within a common numerical framework. We find that all dual configurations exhibit identical spacetime dynamics, while the emitted electromagnetic radiation is related by a rotation of its polarization equal to the duality angle. Our results demonstrate a degeneracy of gravitational observables under electromagnetic duality and provide a concrete mapping between dual configurations at the level of radiation, establishing electromagnetic duality as an organizing principle for dynamical Einstein-Maxwell solutions.