Accretion trajectories in a compact viscous similarity disk
= Accretion trajectories in a compact viscous similarity disk
{title2=$r(t)=Ct^{2/5}+K\sqrt t$}
For the $a=1$ <compact self-similar disk with density-linear viscosity>, radial drift is $\dot r=r/(2t)-R/(10t)$. An integrating factor gives the displayed trajectories. From $0<r_i<R(t_i)$, the arrival time at the origin is $t_i[1-r_i/R(t_i)]^{-10}$, finite for every interior point. The outer-edge trajectory has zero <surface density of a disk> and carries no mass.