  Photon-photon scattering, due to photons interacting with virtual
electron-positron pairs, is an intriguing deviation from classical
electromagnetism predicted by quantum electrodynamics (QED). Apart from being
of fundamental interest in itself, collisions between photons are believed to
be of importance in the vicinity of magnetars, in the present generation
intense lasers, and in intense laser-plasma/matter interactions; the latter
recreating astrophysical conditions in the laboratory. We show that an intense
photon pulse propagating through a radiation gas can self-focus, and under
certain circumstances collapse. This is due to the response of the radiation
background, creating a potential well in which the pulse gets trapped, giving
rise to photonic solitary structures. When the radiation gas intensity has
reached its peak values, the gas releases part of its energy into `photon
wedges', similar to Cherenkov radiation. The results should be of importance
for the present generation of intense lasers and for the understanding of
localized gamma ray bursts in astrophysical environments. They could
furthermore test the predictions of QED, and give means to create ultra-intense
photonic pulses.
