Hidden Momentum and Black Hole Kicks

TL;DR

This paper investigates how hidden electromagnetic momentum in a charge-dipole system can transfer momentum to a black hole during collapse, potentially explaining large black hole recoil velocities observed in simulations.

Contribution

It introduces a model for hidden momentum transfer during black hole formation and suggests a possible electromagnetic origin for black hole superkicks.

Findings

Black hole receives a 0.1% momentum kick from hidden electromagnetic momentum.

Extrapolation indicates a potential role in gravitational superkicks.

Supports electromagnetic mechanisms contributing to black hole recoil velocities.

Abstract

A stationary magnetic dipole immersed in an electric field carries "hidden" mechanical momentum. However, the fate of this momentum if the fields are turned off is unclear. We consider a charge-and-dipole hidden momentum configuration, and turn off the fields by collapsing a null shell onto the system, forming a black hole. In numerical calculations we find that the black hole receives a kick corresponding to 0.1% of the initial stored momentum. When extrapolated to apply to purely gravitational phenomena, this efficiency suggests a role for the hidden momentum kick mechanism in generating the binary black hole "superkicks" observed in numerical simulations of Einstein's equation.