A stage in which several neighboring planetary embryos dominate stirring of surrounding planetesimals and grow in a self-regulated manner. Larger embryos heat their feeding populations more strongly, weakening gravitational focusing and preventing unlimited runaway planetesimal growth. A small number of embryos coexist with many much smaller bodies.
The region of a disk from which a planetary embryo can efficiently accrete solids. Its width depends on gravitational encounters and the surrounding orbital population. Approximating that width by a multiple of the Hill radius gives a useful local isolation mass.
The mass reached after consuming an idealized local annulus of solids. With full annular width and solid surface density , the balance 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.
Growth of planetesimal random orbital motions through gravitational encounters. The word viscous does not denote molecular fluid viscosity here. Stirring competes with gas drag, collisions and dynamical friction in setting the encounter speeds that control gravitational focusing.
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