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Title: THE LARGE-SCALE MAGNETIC FIELDS OF THIN ACCRETION DISKS

Abstract

Large-scale magnetic field threading an accretion disk is a key ingredient in the jet formation model. The most attractive scenario for the origin of such a large-scale field is the advection of the field by the gas in the accretion disk from the interstellar medium or a companion star. However, it is realized that outward diffusion of the accreted field is fast compared with the inward accretion velocity in a geometrically thin accretion disk if the value of the Prandtl number P{sub m} is around unity. In this work, we revisit this problem considering the angular momentum of the disk to be removed predominantly by the magnetically driven outflows. The radial velocity of the disk is significantly increased due to the presence of the outflows. Using a simplified model for the vertical disk structure, we find that even moderately weak fields can cause sufficient angular momentum loss via a magnetic wind to balance outward diffusion. There are two equilibrium points, one at low field strengths corresponding to a plasma-beta at the midplane of order several hundred, and one for strong accreted fields, {beta} {approx} 1. We surmise that the first is relevant for the accretion of weak, possibly external, fieldsmore » through the outer parts of the disk, while the latter one could explain the tendency, observed in full three-dimensional numerical simulations, of strong flux bundles at the centers of disk to stay confined in spite of strong magnetororational instability turbulence surrounding them.« less

Authors:
 [1]
  1. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China)
Publication Date:
OSTI Identifier:
22126962
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 765; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ANGULAR MOMENTUM; ASTRONOMY; ASTROPHYSICS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; DIFFUSION; GALAXIES; JETS; MAGNETIC FIELDS; PLASMA; PLASMA INSTABILITY; PRANDTL NUMBER; RADIAL VELOCITY; STARS; STELLAR WINDS; TURBULENCE

Citation Formats

Xinwu, Cao, and Spruit, Hendrik C., E-mail: cxw@shao.ac.cn, E-mail: henk@mpa-garching.mpg.de. THE LARGE-SCALE MAGNETIC FIELDS OF THIN ACCRETION DISKS. United States: N. p., 2013. Web. doi:10.1088/0004-637X/765/2/149.
Xinwu, Cao, & Spruit, Hendrik C., E-mail: cxw@shao.ac.cn, E-mail: henk@mpa-garching.mpg.de. THE LARGE-SCALE MAGNETIC FIELDS OF THIN ACCRETION DISKS. United States. https://doi.org/10.1088/0004-637X/765/2/149
Xinwu, Cao, and Spruit, Hendrik C., E-mail: cxw@shao.ac.cn, E-mail: henk@mpa-garching.mpg.de. 2013. "THE LARGE-SCALE MAGNETIC FIELDS OF THIN ACCRETION DISKS". United States. https://doi.org/10.1088/0004-637X/765/2/149.
@article{osti_22126962,
title = {THE LARGE-SCALE MAGNETIC FIELDS OF THIN ACCRETION DISKS},
author = {Xinwu, Cao and Spruit, Hendrik C., E-mail: cxw@shao.ac.cn, E-mail: henk@mpa-garching.mpg.de},
abstractNote = {Large-scale magnetic field threading an accretion disk is a key ingredient in the jet formation model. The most attractive scenario for the origin of such a large-scale field is the advection of the field by the gas in the accretion disk from the interstellar medium or a companion star. However, it is realized that outward diffusion of the accreted field is fast compared with the inward accretion velocity in a geometrically thin accretion disk if the value of the Prandtl number P{sub m} is around unity. In this work, we revisit this problem considering the angular momentum of the disk to be removed predominantly by the magnetically driven outflows. The radial velocity of the disk is significantly increased due to the presence of the outflows. Using a simplified model for the vertical disk structure, we find that even moderately weak fields can cause sufficient angular momentum loss via a magnetic wind to balance outward diffusion. There are two equilibrium points, one at low field strengths corresponding to a plasma-beta at the midplane of order several hundred, and one for strong accreted fields, {beta} {approx} 1. We surmise that the first is relevant for the accretion of weak, possibly external, fields through the outer parts of the disk, while the latter one could explain the tendency, observed in full three-dimensional numerical simulations, of strong flux bundles at the centers of disk to stay confined in spite of strong magnetororational instability turbulence surrounding them.},
doi = {10.1088/0004-637X/765/2/149},
url = {https://www.osti.gov/biblio/22126962}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 765,
place = {United States},
year = {Sun Mar 10 00:00:00 EST 2013},
month = {Sun Mar 10 00:00:00 EST 2013}
}