Formation and Propagation of Jets Around Compact Objects

Abstract

The phenomenon of jets is very common among astrophysical objects. Jets appear around supermassive black holes in radio galaxies and quasars, stellar black holes in microquasar or black hole X-ray binaries (BHXBs), around young stellar objects, but also around stellar compact sources as white dwarfs in symbiotic stars and neutron stars in low mass X-ray binaries (LMXBs). In interacting binaries containing compact objects, the secondary — a main-sequence star or red giant — loses matter through a stellar wind or Roche lobe mass overflow. This matter is forced by the gravitational field of the compact primary to form an accretion disc. On the surface of the compact object, explosive nuclear burning causes nova-like outbursts. Through interactions between the accretion disc and the magnetic field of the compact object, matter is accelerated towards the polar regions and ejected as jets. For all objects, the exact mechanism, how jets are launched and the material is accelerated, is not understood very well. A few analytic approaches are developed, but to solve this problem, time-dependant numerical magnetohydrodynamics (MHD) simulations with very high spatial resolution have to be used. Blandford & Payne [BlP82] examined the magnetically forced extraction of energy and angular momentum from the disc and found centrifugally driven outflows, if the angle between the poloidal magnetic field and the disc surface is less than 60°. With increasing distance from the star-disc-system, the toroidal field becomes important, collimating the outflow to jets. Camenzind [Cam90] discovered the first self-consistent model considering all parts of a protostellar star-disc-system.