We present recent developments in the study of an interacting gravitational system of concentric, spherical, mass shells. The existence of two distinct phases is demonstrated. The nature of the transition in the microcanonical, canonical, and grand canonical ensembles is studied both theoretically in terms of mean field theory and via dynamical simulation. Striking differences are found in each environment, especially the last.

• Received 13 July 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.4794