Radio jets and the formation of active galaxies: Accretion avalanches on the torus by the effect of a large-scale magnetic field

We present the results of 2.5-dimensional MHD simulations for a magnetohydrodynamic model of jet formation associated with the formation of active galaxies. We also study the enhanced accretion near the central object of active galactic nuclei. A new factor introduced in our model is the presence of a large-scale poloidal magnetic field that may correspond to either the primordial magnetic field swept into the central region during the galaxy formation process or the central part of a dynamo-generated magnetic field. The differentially rotating disk produced around a central massive object such as a black hole interacts with the large-scale magnetic field, and produces spinning bipolar jets through the production and escape of the magnetic twists propagating into bipolar directions (a form of large-amplitude torsional Alfven waves). The production and escape of these removes angular momentum from the disk material and allows an enhanced accretion rate in the disk. The surface layers of disks accrete faster than the equatorial part because the magnetic braking most effectively affects that layer. The infalling gas spins up, and jet formation strengthens until magnetic reconnection occurring at the inner edge of the disk saturates the process.