There is a well-measured constraint on YMCs that we can apply to predict the upper limit radii for the MPCs. Recent high resolution imagining and spectral studies of YMCs have shown these systems to be in or close to equilibrium at ages of \(\tilde~ 1.5 \leq 3\) years. \cite{Darwin_1900}

This implies that the YMCs must have gone through at least one full crossing time before their presently observed age. Using the crossing time equation, \(t_{cross}=(GMr^{-3}_{vir})^{−1/2}\), and fixing the crossing time to 1 Myr we can solve for \(t\), which is only dependent on the mass. \cite{1999}

For the same clump mass range mentioned for \(r _{\Omega}\) above, \(r _{vir}\) spans from 5.1 to 23.8 pc. This is an important aspect to keep in mind as there is no evidence for YMCs to have a proportionality between mass and radius. \cite{Bedini_2013}