Gas expulsion

The gas here expands homologously — every parcel moves outward by the same factor $S$, so a shell at radius $r$ goes to $rS$ and, by mass conservation, the density thins as$\rho \to \rho/S^{3}$. It falls below the density colorbar and clears from the outside in, while the stars, now decoupled from the gas, stay put. It's a schematic of expulsion, not a feedback simulation: the real thing is anisotropic — champagne flows and blister breakouts along the least-dense channels. That physics is what my radiation-hydrodynamics work models; this piece captures the story it tells.