Turnaround of spherical collapse
= Turnaround of spherical collapse
{title2=$\theta_{\rm ta}=\pi$}
= Spherical-collapse turnaround
{synonym}
A pressureless bound spherical shell first expands, reaches $\dot R=0$ at its maximum radius, and recollapses. In the cycloidal <spherical-collapse model>, turnaround occurs at $\theta=\pi$, with $R_{\max}=2A$ and $t_{\max}=\pi B$. Its mean density is $9\pi^2/16$ times the background density in an <Einstein-de Sitter universe>.