  We demonstrate the existence of gravitational critical phenomena in higher
dimensional electrovac bubble spacetimes. To this end, we study linear
fluctuations about families of static, homogeneous spherically symmetric bubble
spacetimes in Kaluza-Klein theories coupled to a Maxwell field. We prove that
these solutions are linearly unstable and posses a unique unstable mode with a
growth rate that is universal in the sense that it is independent of the family
considered. Furthermore, by a double analytical continuation this mode can be
seen to correspond to marginally stable stationary modes of perturbed black
strings whose periods are integer multiples of the Gregory-Laflamme critical
length. This allow us to rederive recent results about the behavior of the
critical mass for large dimensions and to generalize them to the charged black
string case.
