Homologous rotating collapse ($\Omega \propto R^{-2},F_{\mathrm{cent}}/F_{\mathrm{grav}}\propto R^{-1}$)

During a spherical stellar homology contraction at fixed mass and angular momentum, a constant inertia coefficient gives $I=\alpha M{R}^2$ and solid-body rotation gives $\Omega =J/I\propto R^{-2}$. A fixed fluid label $s=r/R$ retains its enclosed mass and polar angle, so centrifugal acceleration scales as $R^{-3}$ and gravity as $R^{-2}$. Their ratio increases as $R^{-1}$. This assumes spin conservation, not continuous synchronization to an external orbit.

In the spherical approximation, equatorial centrifugal acceleration balances surface gravity when ${\Omega }_c^2{R}_c=GM/R_c^2$. For $I=\alpha M{R}^2$ and conserved angular momentum $J$, this gives the displayed critical radius. Real rotating gas can deform, lose matter and exchange torques before a spherical model remains accurate at this limit.