Hidden Momentum and Black Hole Kicks

Understand

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.