Langevin equation for the collective motions of a binary astrophysical system.

According to Thirring's condition, the thermodynamic equilibrium is not possible between two systems with negative heat capacities. Since the existence of negative heat capacity is a rule rather an exception in astrophysics, we would like to analyze the possibility of the thermodynamic equilibrium for a paradigmatic astrophysical situation: the binary system. The possible explanation arises after decomposing the dynamical variables into internal and collective degrees of freedom, which enables us to reinterpret binary systems as two systems A and B that interact between them through a third low dimensional system C.