Vertical angular momentum transfer from accretion discs and the formation of large-scale collimated jets

• Published in: Plasma physics and controlled fusion Vol. 50; no. 12; p. 124020
• Main Author: Casse, F
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.12.2008
• Subjects: Astrophysics; Galactic Astrophysics; Physics; Sciences of the Universe
• ISSN: 0741-3335; 1361-6587
• DOI: 10.1088/0741-3335/50/12/124020

In this paper I present an overview of the favoured scenario explaining the presence of twin cylindrical astrophysical jets in the vicinity of accretion discs. These jets are made of plasma and host large-scale magnetic fields. The twin jets flow away from the accreting system in opposite directions, perpendicular to the plane of the accretion disc. In the scenario presented in this paper, the accretion disc interacts with the magnetic field in such a way that the disc angular momentum is removed from the disc and transported away along the magnetic field lines. Such a transport is the source of the jet phenomenon as the angular momentum is given back to a tiny amount of material extracted from the disc. This outflow is then powered by the disc rotation as the disc is able to enter an accretion motion where matter releases its gravitational energy. The angular momentum carried by the jet is actually present through the existence of an electric current. In the jet cylindrical geometry, the presence of this current is able to provide a collimating mechanism where the magnetic field pinches the plasma column. This mechanism is very close to the one acting in tokamak reactors. Apart from explaining how the plasma outflow is able to be self-confined by the magnetic field present in the flow, this scenario is also able to explain how jet mass can be accelerated thanks to the magnetohydrodynamics Poynting flux escaping from the disc. In this presentation I finally present the constraints arising from the scenario, in particular upon the turbulent transport coefficient required to get a steady structure.