Magnetic Fields, Disk Winds and Jets in Astrophysics

Abstract

Jets occur in many astrophysical systems that contain accretion disk of some kind. The fundamental parameters of protostellar and cosmic jets are therefore related in some way to the properties of the very central object and its accretion disk. The majority of jet formation models is nowadays based on magnetohydrodynamic processes in geometrically thin disks. In rapidly rotating star-disk systems magnetized plasma outflows can essentially be driven by two different processes: (i) the magnetization of the accretion disk itself will accelerate disk winds to supermagnetosonic speeds, and (ii) a magnetized rapid rotor in interaction with its ambient accretion disk will drive outflows from the boundary layer. Magnetized winds ejected from the surface of the disk will be collimated by magnetic pinch forces on scales somewhat larger than the light cylinder of the rnagnetosphere. Despite a widespread belief in the astrophysical community, the rapid rotation of the rnagnetosphere in protostellar systems, systems containing neutron stars and accretion disks around supermassive objects essentially forbids the use of the Newtonian approximation. When relativistic MHD is used, the slow jets in protostellar systems and the relativistic quasar jets are naturally formed in the rapidly rotating magnetospheres of the corresponding accretion disks.