One of the Holy Grails of observational astronomy is to confirm the prediction that black holes in the Universe are described by the Kerr solution of Einstein’s field equations of general relativity. I served as Guest Editor for a General Relativity and Gravitation Topical Collection which provides a status report of theoretical and experimental progress towards confirming the “Kerr paradigm” through X-ray astronomy, gravitational lensing, stellar tidal disruption events, superradiance, and gravitational-wave observations of black hole binary mergers.
