Cosmic balloons

Cosmic balloons, consisting of relativistic particles trapped inside a spherical domain wall, may be created in the early universe. We calculate the balloon mass $M$ as a function of the radius $R$ and the energy density profile, $ρ (r)$ , including the effects of gravity. At the maximum balloon mass $2 G M / R \approx 0.52$ for any value of the mass density of the wall.