Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars
The standard model for turbulent shear viscosity in accretion disks is based on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. This implies that the turbulent stress must be negative and thus transport angular momentum inwards, in...
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2013-04-01
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Online Access: | http://dx.doi.org/10.1051/epjconf/20134604004 |
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doaj-90d34a2d2d524867866cebab248d963c2021-08-02T14:37:08ZengEDP SciencesEPJ Web of Conferences2100-014X2013-04-01460400410.1051/epjconf/20134604004Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized StarsPessah Martin E.Chan Chi-kwanThe standard model for turbulent shear viscosity in accretion disks is based on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. This implies that the turbulent stress must be negative and thus transport angular momentum inwards, in the boundary layer where the accretion disk meets the surface of a weakly magnetized star. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. Motivated by the need of a deeper understanding of the behavior of an MHD fluid in a differentially rotating background that deviates from a Keplerian profile, we study the dynamics of MHD waves in configurations that are stable to the standard MRI. Employing the shearing-sheet framework, we show that transient amplification of shearing MHD waves can generate magnetic energy without leading to a substantial generation of hydromagnetic stresses. While these results are in agreement with numerical simulations, they emphasize the need to better understand the mechanism for angular momentum transport in the inner disk regions on more solid grounds. http://dx.doi.org/10.1051/epjconf/20134604004 |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Pessah Martin E. Chan Chi-kwan |
spellingShingle |
Pessah Martin E. Chan Chi-kwan Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars EPJ Web of Conferences |
author_facet |
Pessah Martin E. Chan Chi-kwan |
author_sort |
Pessah Martin E. |
title |
Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars |
title_short |
Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars |
title_full |
Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars |
title_fullStr |
Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars |
title_full_unstemmed |
Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars |
title_sort |
angular momentum transport in accretion disk boundary layers around weakly magnetized stars |
publisher |
EDP Sciences |
series |
EPJ Web of Conferences |
issn |
2100-014X |
publishDate |
2013-04-01 |
description |
The standard model for turbulent shear viscosity in accretion disks is based on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. This implies that the turbulent stress must be negative and thus transport angular momentum inwards, in the boundary layer where the accretion disk meets the surface of a weakly magnetized star. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. Motivated by the need of a deeper understanding of the behavior of an MHD fluid in a differentially rotating background that deviates from a Keplerian profile, we study the dynamics of MHD waves in configurations that are stable to the standard MRI. Employing the shearing-sheet framework, we show that transient amplification of shearing MHD waves can generate magnetic energy without leading to a substantial generation of hydromagnetic stresses. While these results are in agreement with numerical simulations, they emphasize the need to better understand the mechanism for angular momentum transport in the inner disk regions on more solid grounds. |
url |
http://dx.doi.org/10.1051/epjconf/20134604004 |
work_keys_str_mv |
AT pessahmartine angularmomentumtransportinaccretiondiskboundarylayersaroundweaklymagnetizedstars AT chanchikwan angularmomentumtransportinaccretiondiskboundarylayersaroundweaklymagnetizedstars |
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1721231145503293440 |