2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/202243An effective action is obtained for the area and mass aspect of a thin shell of radiating self-gravitating matter. On following a mini-superspace approach, the geometry of the embedding space-time is not dynamical but fixed to be either Minkowski or Schwarzschild inside the shell and Vaidya in the external space filled with radiation. The Euler-Lagrange equations of motion are discussed and shown to entail the expected invariance of the effective Lagrangian under time-reparametrization. They are equivalent to the usual junction equations and suggest a macroscopic quasi-static thermodynamic description.LATeX, 20 pages, 2 FigsGeneral Relativity and Quantum Cosmologytext