Non-Equilibrium Structures in Dissipative, Self-Gravitating Systems

Abstract

Self-gravitating systems often reveal very inhomogeneous structures. These structures are maintained over time-scales much longer than any relevant time-scale associated with internal physical factors, such as cooling or free-fall times would suggest. Structures diverging from the classical thermodynamical equilibrium and revealing a certain degree of order are well known in laboratory hydrodynamics and chemistry. Experimental and theoretical studies demonstrate that such structures may develop in non-linear systems maintained from equilibrium. Near equilibrium the degree of order is not very prominent. But after passing a critical distance from equilibrium, the thermodynamical branch becomes unstable and fluctuations can lead the system to more stable and often more organized states. The underlying concepts such as dissipative structures and self-organization are well known and extensively studied (see e.g. Nicolis & Prigogine, 1977, Self-organization in non-equilibrium systems, Wiley, New York). But, despite their popularity, they are until now only little studied in the context of self-gravitating astrophysical systems. Taking up some of the previous ideas, we build thus a simple model of a self-gravitating open system.