  We show that static and oscillating photon bubbles can be excited by diffused
light in the laser cooled matter confined in a magneto-optical trap (MOT). The
bubble instability is due to the coupling between the radiation field and the
mean field oscillations of the ultra-cold gas, and it can provide a source for
low frequency turbulence. We consider a diffusion dominated regime, which can
be described by a radiation transport equation, coupled with the mean field
equations for the cold atom gas. A perturbative analysis shows the occurrence
of two different regimes with either oscillating or purely growing bubbles.
This work could also be useful to understand similar processes in astrophysics.
