Schematics of the influence of viscosity on the MRI condition |$0<\tilde{k}<\tilde{k}_{{\rm cr}}$|⁠. Shown are curves of the imaginary part of |$\tilde{\omega }$| as a function of the dimensionless wavenumber |$\tilde{k}^2$|⁠. With increasing viscosity, the MRI interval shifts to the left and shrink (see also fig. 1 in Pessah & Chen 2008).