age = 10.0 kyr
This simulation models the expanding, filamentary shockwave of a supernova remnant — the real phenomenon behind the Witch's Broom Nebula (NGC 6960), part of the Veil Nebula in Cygnus. A supernova blasts a shell of hot gas outward at thousands of kilometers per second; as that shock sweeps up and compresses the surrounding interstellar medium, the swept-up gas is shock-heated and ionized, glowing in the same emission lines seen in the real object — red hydrogen-alpha at the wispier, less-compressed edge and blue-green doubly-ionized oxygen where compression is highest. Rather than a uniform expanding circle, the shell is built from procedurally generated whip-like filaments whose shape responds to the interstellar magnetic field, giving the thin, twisted structure that makes the real nebula so recognizable. Adjust the time since the supernova to watch the shell expand and decelerate, the ambient ISM density to control how bright and compressed the filaments are, and the magnetic field strength to see the filaments twist and align.