Thermal stability of selfgravitating, optically thin accretion disks
Abstract
In the dynamics of accretion disks, the presence of collective effects associated with the selfgravity of the disk is expected to affect not only the momentum transport, but also the relevant energy balance equations, which could differ substantially from the nonselfgravitating case. Here we follow the model that, when the disk is sufficiently cold, the stirring due to Jeansrelated instabilities acts as a source of effective heating. The corresponding reformulation of the energy equations allows us to: (i) demonstrate how selfregulation can be established, so that the stability parameter Q is maintained close to a threshold value, with weak dependence on radius; (ii) rediscuss the opacity properties in the selfgravitating regime. In particular, we show that, if cooling is dominated by bremsstrahlung, an optically thin stationary accretion solution is thermally stable, even in the nonadvective case, provided the disk is selfgravitating. The details of the cooling function have little effect on the structure of such accretion disk, which is in any case induced by selfgravity to selfregulate. This condition of selfgravitating accretion is expected to be appropriate for the outer regions of many disks of astrophysical interest. With the reformulation of the energy equations described in this paper, we have also secured: (iii) a starting point for the study of the emission properties of selfgravitating accretion disks; (iv) a tool to analyze the structure of the transition region, where the disk becomes selfgravitating.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 April 2001
 DOI:
 10.1051/00046361:20010224
 arXiv:
 arXiv:astroph/0102171
 Bibcode:
 2001A&A...370..342B
 Keywords:

 ACCRETION;
 ACCRETION DISKS;
 GRAVITATION;
 HYDRODYNAMICS;
 INSTABILITIES;
 Astrophysics
 EPrint:
 9 pages, 5 figures, accepted by A&