On the Maximal Value of the Turbulent alpha-Parameter in Accretion Discs

TL;DR

This paper suggests that reducing turbulence dimensionality from three to two dimensions can significantly increase the effective turbulent viscosity in accretion disks, aligning better with observational data but still falling short of observed values.

Contribution

It demonstrates that two-dimensional turbulence models can produce higher alpha-parameters, offering a potential explanation for observed accretion disk viscosities.

Findings

Effective turbulent viscosity can increase by about 40% in 2D turbulence.

Maximum alpha-parameter up to 0.25 M_t^2 aligns better with observations.

Observed alpha-values remain several times higher than model predictions.

Abstract

In this short paper we show that making turbulence two- rather than three-dimensional may increase effective turbulent viscosity by about 40%. Dimensionless hydrodynamical viscosity parameter up to \alpha\_{max} = 0.25 M_t^2 may be obtained in this approach, that is in better agreement with the observational data on non-stationary accretion than the values obtained in numerical simulations. However, the \alpha-parameter values known from observations are still several times higher.