Blandford–Znajek Jet Launching
Some black holes launch narrow jets of plasma across vast distances. The Blandford–Znajek process is a leading explanation. It does not rely on exploding gas alone. It taps the spin of the hole through magnetic fields.
A rotating black hole drags spacetime around itself. That effect is frame dragging. If a strong magnetic field threads the horizon, the rotation twists the field. The twist launches an outward electromagnetic flow. Energy and angular momentum leave the hole. Plasma can ride that flow and form a jet.
The power scales with spin and with magnetic flux on the horizon. A faster spin yields a stronger jet, if the field is large enough. The field itself is usually brought in by an accretion disk. Gas spirals inward and carries flux with it. The hole then acts like a spinning conductor in a magnetosphere.
The outgoing energy is often a Poynting flux. Close to the hole the jet may be magnetically dominated. Farther out the magnetic energy can convert into particle kinetic energy. Radio lobes and X-ray jets then become visible.
The mechanism needs three ingredients. There must be a spinning hole. There must be enough magnetic flux. There must be a way to keep that flux on the horizon. Thick disks and magnetically arrested disks are good candidates. Weak fields produce little jet power.
Observations support the picture in outline. Powerful jets often sit on rapidly spinning holes. Event Horizon Telescope images of M87 show a magnetised flow near the shadow. Numerical simulations also launch jets when spin and flux are high. Details of particle loading and dissipation remain open.
Blandford–Znajek launching therefore links gravity to electromagnetism. Rotation stored in spacetime becomes a directed beam. That conversion helps explain why some black holes stay quiet and others light up entire galaxies.