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Activity of Rotating Magnetospheres in AGNs: Collimated Propagation of MHD Waves near a Black Hole
Author(s) -
HIROTANI Kouichi,
TOMIMATSU Akira
Publication year - 1995
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1995.tb17604.x
Subject(s) - physics , magnetohydrodynamics , magnetohydrodynamic drive , magnetic field , lorentz force , polar , classical mechanics , computational physics , schwarzschild radius , plasma , field line , mechanics , gravitation , astronomy , quantum mechanics
Abstract We have studied non‐stationary and axisymmetric perturbations of a magnetohydrodynamic accretion onto a rotating (Kerr) black hole. Assuming that the magnetic field dominates the plasma accretion, we find that the meridional current becomes large near the fast‐magnetosonic surface located close to the horizon. This is due to the effects of the particle's inertia and the strong gravity near the horizon. As a consequence, the fluid suffers a large radial acceleration resulting from the Lorentz force, and becomes highly variable compared with the electromagnetic field there. In fact, we further find an interesting perturbed structure of the plasma velocity with a large peak in some narrow region just beyond the fast‐magnetosonic surface. If the critical surface has an oblate shape for radial poloidal field lines, this perturbation of plasma motion is induced by outgoing waves propagating from the equatorial super‐fast‐magnetosonic region to the polar sub‐fast‐magnetosonic one. Thus, the effective acceleration of particles due to the outgoing fast‐magnetosonic waves will work mainly in the polar direction as a mechanism of trigger of jet production in active galactic nuclei.