A new rotating spacetime built by stripping magnetism from a known solution

Starting from the recently found Kerr-Bertotti-Robinson solution, the authors switch off the magnetic field via a limiting procedure to obtain a new vacuum rotating metric — a deformation of Kerr in which the usual asymptotically flat region is replaced by a regular spindle-shaped dome. Despite this non-standard asymptotics, a first law of black hole thermodynamics holds, and several thermodynamic relations are numerically identical to their Kerr counterparts, as though the deformation parameter were invisible. The new metric also acts as a neutral seed for generating distinct magnetized versions of Schwarzschild and Kerr black holes.