Magnetic confinement of the optical jets in young stellar objects

We discuss a model for collimating plasma outflow from a young stellar object via an axial current initiated by collisionally charged dust grains incorporated in the ionized outflow from the central object. The charged grains generate an electric current in response to their greater reaction to the radiation field of the central star and their large mobility with respect to the plasma. This produces a pinching toroidal magnetic field ∼10^-3 G in the base flow. A simple self-similar, steady state MHD solution shows that a well-collimated jet can result, when β = c²_s/v²_A ≲ 1 at the critical point in the flow, provided this pinch is only marginally overbalanced there by the gas pressure and centrifugal acceleration associated with any rotation of the jet.