THEORIA-PRISCO: Fons et Origo Veritatis — Paper III: The Dampfkessel Effect: Thermal Dominance in Stellar Feedback

Applying the parameter-free Meta-Equation to astrophysics, we demonstrate that the classical assumption of radiation-pressure-driven expansion in HII regions fails mathematically. Using new 21-cm data of the Orion Nebula, we prove that expansion is driven by the thermal pressure of the photoionized gas (600 times stronger than radiation pressure). We identify this as the Dampfkessel (Steam Boiler) Effect, universal across Orion, NGC 3603, and 30 Doradus. This is Paper III of the THEORIA-PRISCO series. All code, derivations, and data are available for public verification.