  Massively parallel ionization of many atoms in a cluster or bio-molecule is
identified as new phenomenon of light-matter interaction which becomes feasible
through short and intense FEL pulses. Almost simultaneously emitted from the
illuminated target the photo-electrons can have such a high density that they
interact substantially even after photo-ionization. This interaction results in
a characteristic electron spectrum which can be interpreted as convolution of a
mean-field electron dynamics and binary electron-electron collisions. We
demonstrate that this universal spectrum can be obtained analytically by
summing synthetic two-body Coulomb collision events. Moreover, we propose an
experiment with hydrogen clusters to observe massively parallel ionization.
