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On magnetohydrodynamic turbulence and angular momentum transport in accretion disk boundary layers

Published online by Cambridge University Press:  18 July 2013

Chi-kwan Chan  and
Martin E. Pessah
Chi-kwan Chan
Affiliation:
NORDITA, Roslagstullsbacken 23, 106 91 Stockholm, Sweden email: ckch@nordita.org
Martin E. Pessah
Affiliation:
Niels Bohr International Academy, Niels Bohr Institute Blegdamsvej 17, 2100 Copenhagen Ø, Denmark email: mpessah@nbi.dk
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Abstract

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The physical modeling of the accretion disk boundary layer, the region where the disk meets the surface of the accreting star, usually relies on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity, widely adopted in astrophysics, satisfies this assumption by construction. 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 is inefficient in this inner disk region. I will discuss the results of a recent study on the generation of hydromagnetic stresses and energy density in the boundary layer around a weakly magnetized star. Our findings suggest that although magnetic energy density can be significantly amplified in this region, angular momentum transport is rather inefficient. This seems consistent with the results obtained in numerical simulations and suggests that the detailed structure of turbulent MHD boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.

Keywords

accretion disksMHDturbulence
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 8 , Symposium S294: Solar and Astrophysical Dynamos and Magnetic Activity , August 2012 , pp. 349 - 352
Copyright
Copyright © International Astronomical Union 2013 

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