Open AccessOn why discs generate magnetic towers and collimate jets
Author(s) -
LyndenBell D.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06506.x
Subject(s) - physics , accretion (finance) , magnetic field , pinch , mechanics , twist , magnetohydrodynamics , slippage , pressure gradient , collimated light , accretion disc , magnetic pressure , magnetic energy , astrophysics , classical mechanics , optics , geometry , magnetization , nuclear physics , laser , mathematics , structural engineering , quantum mechanics , engineering
We show that accretion discs with magnetic fields in them ought to make jets provided that their electrical conductivity prevents slippage and there is an ambient pressure in their surroundings. We study equilibria of highly wound magnetic structures. General Energy theorems demonstrate that they form tall magnetic towers, the height of which grows with every turn at a velocity related to the circular velocity in the accretion disc. The pinch effect amplifies the magnetic pressures toward the axis of the towers, the stability of which is briefly considered. We give solutions for all twist profiles Φ( P ) =Ω( P ) t and for any external pressure distribution p ( z ). The force‐free currents are given by and we show that the constant pressure case gives which leads to analytic solutions for the fields.