Astrophysical bounds on photons escaping into extra dimensions

In a class of extra-dimensional models with a warped metric and a single brane the photon can be localized on the brane by gravity only. An intriguing feature of these models is the possibility of the photon escaping into the extra dimensions. The search for this effect has motivated the present round of precision ortho-positronium decay experiments. We point out that in this framework a photon in plasma should be metastable, and we consider what this implies for cooling of globular cluster stars and core-collapse supernovae. The resulting bounds on the model parameter exceed the possible reach of ortho-positronium experiments by many orders of magnitude.