Keplerian viscous diffusion equation
= Keplerian viscous diffusion equation
{c}
{title2=$\Sigma_t=(3/r)\partial_r[r^{1/2}\partial_r(r^{1/2}\bar\nu\Sigma)]$}
Use $l=\sqrt{GM_*r}$ and $\Omega'=-(3/2)\Omega/r$ in the <vertically averaged viscous disk equations>. The radial drift is $v_r=-3(\Sigma\sqrt r)^{-1}\partial_r(\sqrt r\bar\nu\Sigma)$. <Conservation of mass> gives this nonlinear <diffusion equation>. It assumes the central rotation law remains fixed and excludes wind/surface <torque> terms.