Free-fall timescale
= Free-fall timescale
{title2=$t_{\rm ff}$}
The gravitational collapse scale $t_{\rm ff}\sim\sqrt{R^3/(GM)}$. Radial fall from rest at $R$ to a fixed central <point mass> has the exact time $\pi\sqrt{R^3/(GM)}/(2\sqrt2)$.
= Free-fall timescale
{title2=$t_{\rm ff}$}
The gravitational collapse scale $t_{\rm ff}\sim\sqrt{R^3/(GM)}$. Radial fall from rest at $R$ to a fixed central <point mass> has the exact time $\pi\sqrt{R^3/(GM)}/(2\sqrt2)$.