skip to main content

SciTech ConnectSciTech Connect

Title: VERTICAL STRUCTURE AND CORONAL POWER OF ACCRETION DISKS POWERED BY MAGNETOROTATIONAL-INSTABILITY TURBULENCE

In this paper, we consider two outstanding intertwined problems in modern high-energy astrophysics: (1) the vertical-thermal structure of an optically thick accretion disk heated by the dissipation of magnetohydrodynamic turbulence driven by the magnetorotational instability (MRI), and (2) determining the fraction of the accretion power released in the corona above the disk. For simplicity, we consider a gas-pressure-dominated disk and assume a constant opacity. We argue that the local turbulent dissipation rate due to the disruption of the MRI channel flows by secondary parasitic instabilities should be uniform across most of the disk, almost up to the disk photosphere. We then obtain a self-consistent analytical solution for the vertical thermal structure of the disk, governed by the balance between the heating by MRI turbulence and the cooling by radiative diffusion. Next, we argue that the coronal power fraction is determined by the competition between the Parker instability, viewed as a parasitic instability feeding off of MRI channel flows, and other parasitic instabilities. We show that the Parker instability inevitably becomes important near the disk surface, leading to a certain lower limit on the coronal power. While most of the analysis in this paper focuses on the case of a diskmore » threaded by an externally imposed vertical magnetic field, we also discuss the zero net flux case, in which the magnetic field is produced by the MRI dynamo itself, and show that most of our arguments and conclusions should be valid in this case as well.« less
Authors:
 [1]
  1. Center for Integrated Plasma Studies, Physics Department, University of Colorado, Boulder, CO 80309 (United States)
Publication Date:
OSTI Identifier:
22270843
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 775; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ANALYTICAL SOLUTION; ASTRONOMY; ASTROPHYSICS; DIFFUSION; INSTABILITY; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; OPACITY; PHOTOSPHERE; RADIANT HEAT TRANSFER; TURBULENCE