Critical mass-to-flux ratio
= Critical mass-to-flux ratio
{title2=$(M/\Phi)_{\rm crit}=\lambda/\sqrt{\mu_0G}$}
For fixed cloud shape, gravitational energy scales as $-C_gGM^2/L$ and <magnetic energy> as $C_B\Phi^2/(\mu_0L)$. The magnetic-criticality threshold for negligible <pressure> is $M/\Phi>\sqrt{C_B/C_g}/\sqrt{\mu_0G}$. Ideal flux freezing keeps this ratio fixed during homologous collapse; geometry determines the numerical coefficient.