FRONT DYNAMICS IN THERMALLY BISTABLE ASTROPHYSICAL FLUIDS

The nonlinear development of thermal bistability in fluids is investig ated. One-dimensional models of interacting fronts, treated with the h elp of singular perturbation theory yield for exponentially (in their size) long time on the way to phase separation. Spatial and temporal p erturbation of the cooling may give rise to complex steady patterns. I n two dimensions we perform numerical simulations and find for the pur ely thermal case and for the hydrodynamic case with open boundaries a qualitatively similar behavior - overall growth of the majority domain as a power of the time. Again, stationary complex pattern may be achi eved by locking onto spatio-temporal perturbations The hydrodynamic ca se differs from the purely thermal case in the value of the dynamical exponent (the power with which the correlation length grows in time). The probability of occurrence of critical conditions in an observed as trophysical system is assessed using statistical considerations.