SELF-ORGANIZATION OF COSMIC-RADIATION PRESSURE INSTABILITY

The instability caused by radiation pressure from uniformly distributed emitters in a continuous dissipative absorbing medium is analyzed in the absence of other astrophysical forces. Three analytical descriptions of this idealized system are outlined: mock gravity, linear instability theory, and a symmetric bubble model. These models are used to describe the behavior of an infinite, statistically homogeneous unstable expanding absorbing medium after the typical structures become both nonlinear and optically thick. It is argued that the system displays nonlinear self-organizing behavior: the absorbers evolve toward an autocatalytic, temporally self-similar steady state which is statistically independent of initial conditions. In this saturated state the absorbers are concentrated in thin walls around empty bubbles; as the instability develops the big bubbles get bigger and the small ones get crushed and disappear. A linear analysis shows that to first order the thin walls are indeed stable structures. It is speculated that this instability may play a role in forming cosmic large-scale structure. Other possible astrophysical sites for the nonlinear instability are briefly summarized.