Hostname: page-component-78c5997874-ndw9j Total loading time: 0 Render date: 2024-11-13T07:10:49.698Z Has data issue: false hasContentIssue false
  • English
  • Français

Magnetic Fields in Thin Accretion Disks Around Black Holes

Published online by Cambridge University Press:  19 July 2016

R. Khanna  and
M. Camenzind
R. Khanna
Affiliation:
Landessternwarte Königstuhl, W-6900 Heidelberg, Germany
M. Camenzind
Affiliation:
Landessternwarte Königstuhl, W-6900 Heidelberg, Germany

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

We study magnetic field topologies and magnetic field strength in a thin accretion disk around a rotating black hole. The magnetic field is assumed to enter the disk at the outer edge and is amplified in the accretion process by differential rotation. This scenario seems likely for AGN, where magnetized plasma from a molecular torus flows into an inner accretion disk.

In nonideal Newtonian magnetohydrodynamics the presence of a rotating central black hole is taken into account by using the form of the Keplerian rotation law valid for Kerr geometry outside the marginally stable orbit and a boundary layer, caused by the frame dragging effect, within. In the unstable region close to the hole the turbulent timescale is much larger than the accretion timescale so that the effective magnetic diffusivity, which is large in the disk due to turbulence, is low. As a consequence the poloidal magnetic field lines cross the horizon almost radially in agreement with [1].

We present stationary axisymmetric solutions of the induction equation for vanishing α-effect. Dipolar field structures are most favourable for the generation of fast jets and can effectively contribute to the heating of a corona or some X-ray source. Quadrupolar field structures may also drive jets, however the field strength is considerably lower and therefore also the energy that can be supplied into a corona or a jet.

Type
5. Magnetic Field Generation in Accretion Disks
Information
Symposium - International Astronomical Union , Volume 157: The Cosmic Dynamo , 1993 , pp. 193 - 196
Copyright
Copyright © Kluwer 1993 

References

1: Thorne, K. S., Price, R.H., Macdonald, D. A.: Black holes, the membrane paradigm, Yale Univ. Press, New Haven.Google Scholar
2: Khanna, R., Camenzind, M.: 1992, Astron. Astrophys. 263, 401.Google Scholar
3: Camenzind, M.: 1990, Magnetized Accretion Disks and the Origin of Bipolar Outflows, Reviews in Modern Astronomy 3.Google Scholar
4: Blandford, R.D., Znajek, R.L.: 1977, Mon. Not. R. astr. Soc. 179, 433.Google Scholar
5: Haehnelt, M., Camenzind, M.: 1992, submitted to Astron. Astrophys .Google Scholar
6: Pounds, K.: 1992, in Physics of AGN, eds. Duschl, W., Wagner, S., Springer-Verlag, Berlin Heidelberg.Google Scholar