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Astron. Astrophys. 326, 1277-1284 (1997)

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On collimation of the outflows in force-free magnetospheres

I. Okamoto

Division of Theoretical Astrophysics, National Astronomical Observatory, Mitaka, Tokyo, 181 Japan

Received 29 August 1996 / Accepted 9 June 1997

Abstract

It is pointed out that "an indeterminacy" claimed to exist in the pulsar equation (Sulkanen & Lovelace 1990) or a "free" function [FORMULA] (Appl & Camenzind 1993a,b) can be uniquely related to the stream function at the boundary of the force-free region to the load region at infinity (Michel 1973b: Okamoto 1974). The form of [FORMULA] is given by [FORMULA] from the plasma conditions at infinity, where [FORMULA] is the angular velocity of field lines. This relation can be interpreted as indicating Ohm's law for the return current from the equatorial region to the polar region on the 'sphere at infinity' with finite resistivity [FORMULA] Ohm, thereby ensuring the current closure. The field structure tends to be asymptotically conical, toward the 'sphere at infinity' and fields fill all the space there. It is argued that force-free models for purely cylindrical jets cannot self-consistently conserve electric current. The role of the plasma conditions in the black hole equation is mentioned as well.

Key words: MHD – ISM: jets and outflows – galaxies: jets – Black hole physics – pulsars: general

Send offprint requests to: I. Okamoto (okamoto@nao.ac.jp)

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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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