# Local stability and global instability in iron-opaque disks

## TL;DR

This paper investigates how the iron opacity bump influences the thermal stability of accretion disks, highlighting the importance of global models over local simulations in understanding disk behavior.

## Contribution

It presents a global time-dependent model analyzing the stabilizing effect of the iron opacity bump on accretion disk stability, extending previous local simulation results.

## Key findings

- Iron opacity bump can stabilize accretion disks at certain conditions.
- Global models reveal stability ranges not seen in local simulations.
- Atomic processes influence disk stability through opacity effects.

## Abstract

The thermal stability of accretion disk and the possibility to see a limit-cycle behaviour strongly depends on the ability of the disk plasma to cool down. Various processes connected with radiation-matter interaction appearing in hot accretion disk plasma contribute to opacity. For the case of geometrically thin and optically thick accretion disk, we can estimate the influence of several different components of function \kappa, given by the Roseland mean. In the case of high temperatures, the electron Thomson scattering is dominant. At lower temperatures atomic processes become important. The slope d log \kappa/d log T can have locally stabilizing or destabilizing effect on the disk. Although the local MHD simulation postulate the stabilizing influence of the atomic processes, only the global time-dependent model can reveal the global disk stability range estimation. This is due to global diffusive nature of that processes. In this paper, using previously tested GLADIS code with modified prescription of the viscous dissipation, we examine the stabilizing effect of the Iron Opacity Bump.