Relativistic Dynamos in Magnetospheres of Rotating Compact Objects

Abstract

The kinematic evolution of axisymmetric magnetic fields in rotating magnetospheres of relativistic compact objects is analytically studied, based on relativistic Ohm's law in stationary axisymmetric geometry. By neglecting the poloidal flows of plasma in simplified magnetospheric models, we discuss self-excited dynamos due to the frame-dragging effect (originally pointed out by Khanna & Camenzind), and we propose alternative processes to generate axisymmetric magnetic fields against ohmic dissipation. The first process (which may be called induced excitation) is caused by the help of a background uniform magnetic field in addition to the dragging of inertial frames. It is shown that excited multipolar components of poloidal and azimuthal fields are sustained as stationary modes, and outgoing Poynting flux converges toward the rotation axis. The second one is self-excited dynamo through azimuthal convection current, which is found to be effective if plasma rotation becomes highly relativistic with a sharp gradient in the angular velocity. In this case no frame-dragging effect is needed, and the coupling between charge separation and plasma rotation becomes important. We discuss briefly the results in relation to active phenomena in the relativistic magnetospheres.Comment: 16 pages, AASLaTeX macros v4.

The general relativistic magnetohydrodynamic dynamo equation

“…The interaction of gravitational waves, and other general relativistic gravity effects, with electromagnetic fields and plasmas has attracted broad interest over the past few years, because of its possible application to both astrophysics and cosmology (e.g. Blandford & Znajek 1977; Thorne & Macdonald 1982; Macdonald & Thorne 1982; Tsagas & Barrow 1997; Tomimatsu 2000; Marklund, Dunsby & Brodin 2000; Tsagas & Mbbrtens 2000; Tsagas 2001; Tsagas et al 2003; Clarkson et al 2004). Here, we will derive the general form of the dynamo equation, using the 1 + 3 covariant formalism (Ellis & van Elst 1998), and analyse its coupling to matter and space–time geometry.…”

Magnetic Neutral Points and Electric Lines of Force in Strong Gravity of a Rotating Black Hole

“…Non-vacuum fields are more complicated and have been [24] notice that high conductivity of the medium changes the field expulsion properties of the horizon. On the other hand, only few aspects of the misaligned BH magnetic fields have been explored so far [37,42]. This is because of an extra complexity caused by the frame-dragging [1,18].…”

“…On the other hand, only few aspects of the misaligned BH magnetic fields have been explored so far [37,42]. This is because of an extra complexity caused by the frame-dragging [1,18].…”

Magnetic layers and neutral points near a rotating black hole

“…The magnetic field is directed in a general angle with respect to the BH rotation axis. Only a few aspects of these misaligned magnetic fields have been explored so far (see Tomimatsu (2000) and Neronov and Aharonian (2007)). The transversal component is wound up around the horizon, and it is not expelled out of the horizon (i.e., the transversal magnetic flux across the horizon does not vanish even in the extremely rotating case, Bičák et al 2007).…”