On why discs generate magnetic towers and collimate jets

By D. Lynden-Bell. 2002

196 citations recorded by the source corpus.

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 j = α(P)B and we show that the constant pressure case gives α P - 1 /2 which leads to analytic solutions for the fields.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/940f6694ef7bf354871bfd312b3d37bbf7c5f46c

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Citations in the corpus

Magnetic tower outflows from a radial wire array Z-pinch (2005, background): “In Lynden-Bell 1996, and Lynden-Bell 2003 a series of heuristic magneto-static models were developed which explored the fundamental structure of such jets called magnetic towers.”
The Influence of Magnetic Field Geometry on the Evolution of Black Hole Accretion Flows: Similar Disks, Drastically Different Jets (2007, background): “As discussed in Hawley & Krolik (2006), a magnetic tower forms, similar to the one predicted on analytic grounds (Lynden-Bell 2003) and seen in other simulations (Kato et al. 2004).”
Accretion disc viscosity: how big is alpha? (2007, background): “In accretion discs, as stressed by Ustyogova et al. (2000) and by Lynden-Bell (2003), all these phenomena are likely to be present but driven much more vigorously by the strong disc shear and by the fact that the disc is rotating so rapidly that it is centrifugally supported (and so disc velocities…”
Outflows and Jets from Collapsing Magnetized Cloud Cores (2005, methodology): “The fact that toroidal field component dominates the poloidal component in the outflow region shows that the large scale outflow is driven by (toroidal) magnetic pressure and confined by by the same toroidal field structure as shown in Lynden-Bell (2003).”
Magnetic processes in a collapsing dense core I. Accretion and ejection (2007, result): “(21) This expression is somehow similar to some of the expressions obtained by Lynden-Bell (1996, 2003) although his analysis is more sophisticated since the explicit value of the tower radius is taken into account.”
A NEW JEANS RESOLUTION CRITERION FOR (M)HD SIMULATIONS OF SELF-GRAVITATING GAS: APPLICATION TO MAGNETIC FIELD AMPLIFICATION BY GRAVITY-DRIVEN TURBULENCE (2011, background): “…which are launched by a tower of magnetic pressure and/or by a centrifugal magnetic field (e.g., Blandford & Payne 1982; Pudritz & Norman 1983; Contopoulos 1995; Lynden-Bell 2003; Machida et al. 2006; Banerjee & Pudritz 2006, 2007; Duffin & Pudritz 2009, for theoretical work on jets and outflows)5.”
MHD simulations of jet acceleration from Keplerian accretion disks - The effects of disk resistivity (2007, background): “7 propagates vertically along the outflow axis similar to a “magnetic tower” (Li et al. 2001; Lynden-Bell 2003).”
Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit (2007, background): “It is the toroidal field that drives the expansion of the bubble, as in the so-called “magnetic tower” investigated by Lynden-Bell (2003).”
Magnetically Driven Jets in the Kerr Metric (2005, background): “A ‘‘magnetic tower’’ forms, as has previously been predicted on analytic grounds (Lynden-Bell 2003) and seen in other simulations (Kato et al. 2004).”