Open AccessThe fundamental difference between shear alpha viscosity and turbulent magnetorotational stresses
Author(s) -
Pessah Martin E.,
Chan Chikwan,
Psaltis Dimitrios
Publication year - 2008
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2007.12574.x
Subject(s) - magnetorotational instability , physics , turbulence , magnetohydrodynamic drive , shearing (physics) , mechanics , angular momentum , accretion (finance) , classical mechanics , shear (geology) , viscosity , magnetohydrodynamics , astrophysics , magnetic field , thermodynamics , petrology , quantum mechanics , geology
Numerical simulations of turbulent, magnetized, differentially rotating flows driven by the magnetorotational instability (MRI) are often used to calculate the effective values of alpha viscosity that is invoked in analytical models of accretion discs. In this paper, we use various dynamical models of turbulent magnetohydrodynamic stresses, as well as numerical simulations of shearing boxes, to show that angular momentum transport in MRI‐driven accretion discs cannot be described by the standard model for shear viscosity. In particular, we demonstrate that turbulent magnetorotational stresses are not linearly proportional to the local shear and vanish identically for angular velocity profiles that increase outwards.