The Blandford-Znajek mechanism (or Blandford-Znajek process or BZ process) is a means by which a magnetized accretion disk can extract rotational energy from a spinning black hole (BH). It involves a magnetic field generated by the accretion disk, whose field lines thread the black hole's rotating ergosphere, producing twists of the lines from each of the black hole's rotational poles. Charged particles within the cylinder of twisted lines can be accelerated away from the black hole, comprising jets.
The theory was developed in 1977 by Roger Blandford and Roman Znajek, following the development of the Penrose process, another mechanism that could extract BH rotational energy. The BZ process is a possible mechanism by which quasars are powered.