🌌 Nebula Formation Dynamics (2D): Jeans Instability & Gravitational Collapse

The 3D version of this page renders a pretty volumetric nebula cloud, but its particles only drift on a fixed sine-wave wobble around static centers — there is no gravity, no pressure and nothing that could ever actually collapse. This 2D companion builds the real mechanic the title promises: every gas parcel attracts every other parcel through softened Newtonian gravity, computed pairwise every frame, while thermal jitter and turbulent kicks push back like real pressure. A side panel exposes temperature, gravity strength, parcel count and turbulence, and a live readout tracks the cloud's actual mass, density, Jeans mass and virial parameter — so raising the temperature slider visibly halts a collapse in progress, and raising density or gravity visibly restarts one, exactly as the Jeans-instability criterion M > M_J predicts. Parcels that touch merge into growing protostars, letting you watch star formation happen from first principles instead of from a canned animation.