Non-existence of stationary two-black-hole configurations: The degenerate case

Understand

In a preceding paper we examined the question whether the spin-spin repulsion and the gravitational attraction of two aligned sub-extremal black holes can balance each other.

• Based on the solution of a boundary value problem for two separate (Killing-) horizons and a novel black hole criterion we were able to prove the non-existence of the equilibrium configuration in question.
• In this paper we extend the non-existence proof to extremal black holes.