High-resolution parameter study of the vertical shear instability – II: dependence on temperature gradient and cooling time

A certain appeal to the alpha model for turbulence and related viscosity in accretion disks was that one scales Reynolds stresses simply on thermal pressure, assuming driven by a mechanism will attain characteristic Mach number its velocity fluctuations. Besides notion there are different driving angular momentum transport disk, we also find within single instability mechanism, here Vertical Shear Instability, do not linearly scale with pressure. Here demonstrate numerical simulations effect of gas temperature gradient relaxation time average generated non-linear stage instability. We square exponent radial profile at least range $d \log T /d R = [-0.5, -1]$, beyond which pressure height varies too much over simulation domain, provide clear results. Stresses dependent times, provided they longer than $10^{-3}$ orbital periods. The strong dependence viscous local conditions disk (especially temperature, gradient, surface density/optical depth) challenges ideas leading smooth density distributions, opening route structure (ring) formation variable mass accretion.