Magnetocentrifugal Launching

Magnetocentrifugal launching is the mechanism by which plasma is accelerated along rotating magnetic field lines through the action of centrifugal force. It is the physical basis of the Blandford-Payne process, in which accretion disks launch jets into space, and operates in any rotating, magnetized plasma where the field lines are sufficiently inclined from the rotation axis.

When a conducting fluid rotates in a magnetic field, the field lines are frozen into the fluid and co-rotate with it. If the field lines are inclined more than 30 degrees from the vertical, the centrifugal acceleration along the field line exceeds gravity, and material is flung outward along the field line like beads on a rotating wire. The terminal velocity is set by the balance between centrifugal acceleration and magnetic tension.

The process was first analyzed in the context of stellar winds and later applied to accretion disks. It requires that the magnetic field be strong enough to enforce corotation — the plasma must remain frozen to the field lines — but not so strong that it suppresses the launching. This balance defines a parameter regime relevant to active galactic nuclei, protostellar systems, and cataclysmic variables.

The magnetocentrifugal mechanism is one of the most general processes for angular momentum transport in rotating, magnetized systems. The same physics drives the solar wind and the most powerful jets in the universe. The disciplinary separation between stellar astrophysics and AGN physics has obscured this unity, but the equations do not care about our departments.