Left: Shell radius as a function of time normalised to the free-fall time for ϵ_* = 1% (green), 5% (water green), 10% (blue), and 30% (purple). The cloud surface density and metallicity are ${\mathrm{\Sigma }}_g={10}^4{M}_{\odot }{\mathrm{pc}}^{-2}$ and log(Z/Z_⊙) =  − 2, respectively. Both the shell solution (Eq. (2), solid line) and the simulation predictions (dashed) are shown. Right: Same but for the shell velocity.