= Isolation mass
{title2=$M_{\rm iso}=(2\pi B a^2\Sigma_s)^{3/2}/(3M_\star)^{1/2}$}
The <mass> reached after consuming an idealized local annulus of solids. With full annular width $\Delta a=B a[M_{\rm iso}/(3M_\star)]^{1/3}$ and solid <surface density> $\Sigma_s$, the balance $M_{\rm iso}=2\pi a\Delta a\Sigma_s$ gives the displayed value. Radial replenishment, migration and embryo mergers can overcome local isolation; defining the width with a mutual rather than single-body <Hill radius> changes the numerical coefficient.
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