2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/14585A Kerr black hole can flare quasi-periodically, if it is magnetically connected to the accretion disk. The flares extract the rotational energy of the hole. The flaring occurs because the hole twists the magnetic field lines beyond the threshold of the screw instability.8 pages, submitted to ApJAstrophysicstext