Stationary double black hole without naked ring singularity

Understand

Recently double black hole vacuum and electrovacuum metrics attracted attention as exact solutions suitable for visualization of ultra-compact objects beyond the Kerr paradigm.

• However, many of the proposed systems are plagued with ring curvature singularities.
• Here we present a new simple solution of this type which is asymptotically Kerr, has zero electric and magnetic charges, but is endowed with magnetic dipole moment and electric quadrupole moment.
• It is manifestly free of ring singularities, and contains only a mild string-like singularity on the axis corresponding to a distributional energy-momentum tensor.Its main constituents are two extreme co-rotating black holes carrying equal electric andopposite magnetic and NUT charges.