Spherical Collapse: One Function for All Profiles
A drop of ink spreads in a glass of water: its edges move faster than its center, and the drop's shape changes. Likewise, a clump of dark matter collapsing under its own gravity expands unevenly, with different shells flying apart at different speeds. Previously, astrophysicists could accurately describe only the simplest case, a uniform sphere with a sharp boundary, which has a single expansion rate.