On why discs generate magnetic towers and collimate jets

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.

[1]  Bruce Margon,et al.  Observations of SS 433 , 1984 .

[2]  K. Shibata,et al.  A magnetodynamic mechanism for the formation of astrophysical jets. I: Dynamical effects of the relaxation of nonlinear magnetic twists , 1985 .

[3]  A. V. Koldoba,et al.  Dynamics of Magnetic Loops in the Coronae of Accretion Disks , 1998 .

[4]  D. Uzdensky.  Partial Field Opening and Current Sheet Formation in the Disk Magnetosphere , 2002, astro-ph/0201522.

[5]  D. Lynden-Bell,et al.  Galactic Nuclei as Collapsed Old Quasars , 1969, Nature.

[6]  P. Bellan,et al.  A laboratory plasma experiment for studying magnetic dynamics of accretion discs and jets , 2002, astro-ph/0202380.

[7]  C. Norman,et al.  The collimation of magnetized winds , 1989 .

[8]  J. Contopoulos.  A Simple Type of Magnetically Driven Jets: an Astrophysical Plasma Gun , 1995 .

[9]  J. Aly.  On some properties of force-free magnetic fields in infinite regions of space , 1984 .

[10]  R. Pudritz,et al.  Numerical simulations of astrophysical jets from Keplerian discs — III. The effects of mass loading , 1999 .

[11]  I. S. Grant,et al.  Electromagnetic radiation , 1978, Nature.

[12]  A. Bell,et al.  The stability, during formation, of magnetohydrodynamically collimated jets , 1997 .

[13]  M. Rees.  New Interpretation of Extragalactic Radio Sources , 1971, Nature.

[14]  R. Blandford,et al.  Electromagnetic extraction of energy from Kerr black holes , 1977 .

[15]  P. Sturrock.  Maximum Energy of Semi-infinite Magnetic Field Configurations , 1991 .

[16]  Martin J. Rees,et al.  A ‘Twin-Exhaust’ Model for Double Radio Sources , 1974 .

[17]  A. Bell,et al.  Magnetohydrodynamic jet formation , 1995 .

[18]  Martin J. Rees,et al.  Theory of extragalactic radio sources , 1984 .

[19]  P. A. G. Scheuer,et al.  Models of Extragalactic Radio Sources with a Continuous Energy Supply from a Central Object , 1974 .

[20]  R. Blandford,et al.  Hydromagnetic flows from accretion discs and the production of radio jets , 1982 .

[21]  J. M. Leblanc,et al.  A Numerical Example of the Collapse of a Rotating Magnetized Star , 1970 .

[22]  K. Shibata,et al.  A magnetodynamic mechanism for the formation of astrophysical jets. II: Dynamical processes in the accretion of magnetized mass in rotation , 1986 .

[23]  W. Baade.  Polarization in the Jet of Messier 87. , 1956 .

[24]  Colin Norman,et al.  Bipolar hydromagnetic winds from disks around protostellar objects , 1986 .

[25]  D. Lynden-Bell,et al.  The Evolution of viscous discs and the origin of the nebular variables. , 1974 .

[26]  C. Barnes,et al.  Force-free magnetic-field structures and their role in solar activity. , 1972 .

[27]  A. Eddington,et al.  The Internal Constitution of the Stars , 1920, Nature.

[28]  I. Okamoto.  Do magnetized winds self-collimate? , 1999 .

[29]  H. Berk,et al.  Magnetically driven jets and winds , 1991 .

[30]  D. Lynden-Bell,et al.  Self-similar solutions up to flashpoint in highly wound magnetostatics , 1994 .

[31]  J. Aly,et al.  Nonequilibrium in sheared axisymmetric force-free magnetic fields , 1995 .

[32]  J. Stone,et al.  Episodic jets from black holes and protostars , 1997, Nature.

[33]  R. Lovelace,et al.  Dynamo model of double radio sources , 1976, Nature.

[34]  Magnetocentrifugal Launching of Jets from Accretion Disks. I. Cold Axisymmetric Flows , 1999, astro-ph/9902200.

[35]  T. Mahoney,et al.  The central KPC of starbursts and AGN : the la Palma connection : proceedings of a confernce held in Los Cancajos, la Palma, Spain, 7-11 May 2001 , 2001 .

[36]  D. Uzdensky,et al.  Magnetically Linked Star-Disk Systems. II. Effects of Plasma Inertia and Reconnection in the Magnetosphere , 2002 .

[37]  J. Contopoulos.  Force-free Self-similar Magnetically Driven Relativistic Jets , 1995 .

[38]  E. Parker.  Cosmic rays and their formation of a galactic halo. , 1965 .

[39]  G. Burbidge.  The Nuclei of Galaxies , 1970 .

[40]  M. Rees,et al.  On Quasars, Dust and the Galactic Centre , 1971 .

[41]  I. Mirabel,et al.  Sources of Relativistic Jets in the Galaxy , 1999, astro-ph/9902062.

[42]  D. Lynden-Bell.  Magnetic collimation by accretion discs of quasars and stars , 1996 .