Thermodynamics of a two-dimensionnal unbounded self-gravitating system

Abstract : The thermodynamics of a two-dimensional self-gravitating system occupying the whole plane is considered in the mean-field approximation. First, it is proven that, if the number N of particles and the total energy E are imposed as the only external constraints, then the entropy admits the least upper bound S+(N,E)=2E/N+N ln(eπ2) (in appropriate units). Moreover, there does exist a unique state of maximum entropy, which is characterized by a Maxwellian distribution function with a temperature T=N/2 independent of E. Next, it is shown that, if the total angular momentum J is imposed as a further constraint, the largest possible value of the entropy does not change, and there is no admissible state of maximum entropy, but in the case J=0. Finally, some inequalities satisfied by a class of so-called H functions and related generalized entropies are given.
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Jérôme Perez, Jean-Jacques Aly. Thermodynamics of a two-dimensionnal unbounded self-gravitating system. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, American Physical Society, 1999, 60, pp.5185. ⟨10.1103/PhysRevE.60.5185⟩. ⟨hal-01010745⟩

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