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Astron. Astrophys. 360, L17-L20 (2000)


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Letter to the Editor

Multi-layer accretion disks around black holes and formation of a hot ion-torus

A. Hujeirat and M. Camenzind

Landessternwarte-Königstuhl, Königsstuhl 12, 69117 Heidelberg, Germany

Received 17 May 2000 / Accepted 15 July 2000

Abstract

We present the first 2D steady-state numerical radiative hydrodynamical calculations showing the formation of a low-density hot torus in the very inner region of accretion disks around a black hole. The inner part of the disk is found to be thermally unstable when Bremsstrahlung is the dominant cooling mechanism. Within the parameter regime used and in the absence of magnetic fields, the torus-plasma is highly time-dependent with supersonic oscillating motion with respect to the electron temperature.

When the soft photons from the disk comptonize the electrons efficiently, the ion-pressure supported torus shrinks in volume, but decelerates further the inward motion into the hole. We speculate that magnetic fields would stabilize the tori by lowering its energy package through initiating jets and/or outflows.

In the outer region, we find that the scale height of the angular velocity [FORMULA] largely exceeds the scale height of the density [FORMULA]. This yields a multi-layer flow-structure in the vertical direction which slows the inwards motion into the BH significantly, enhancing further the formation of the hot torus.

Key words: Black holes - Accretion disks – Boundary layers – relativistic hydrodynamics – Radiation

Send offprint requests to: A. Hujeirat

© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000

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