@chi]) and simulations [@pet]. We chose the microcanonical ensemble as the most fundamental one for the long-range interacting systems. It has to be noted that the considered system is strongly ensemble-dependent: While the nature of the uniform state is the same in both microcanonical and canonical ensembles (apart form the difference in their stability range), the core-halo states and the collapse itself in these ensembles have very little in common with each other [@dv; @chs].

A MF phase diagram of the considered self-attracting microcanonical system is presented in Fig. (\[fig\_mf\]) [@usg; @chi].

![\[fig\_mf\] Plots of entropy $s(\e)$ (solid line) and inverse temperature $\b(\e)=ds/d\e$ (dashed line) vs. energy $\e$ for a system with a gravitational phase transition and a short-range cutoff.](fig1.eps){width=".45\textwidth"}

High- and low-energy branches terminating at the energies $\e_{coll}$ and $\e_{expl}$ correspond to the uniform and core-halo states. The energy $\e^*$ where the entropies of the core-halo and uniform states are equal is the energy of the true phase transition; the uniform and the core-halo states are metastable in the energy intervals $(\e_{coll},\e^*)$ and $(\e^*,\e_{expl})$, respectively. However, for the phase transition to occur at or near $\e^*$, a macroscopic-scale fluctuation with prohibitively low entropy is required. Consequently, the metastable branches 