title: Self-organized relaxation in a collisionless gravitating system.
abstract: We propose the self-organized relaxation process which drives a collisionless self-gravitating system to the equilibrium state satisfying local virial (LV) relation. During the violent relaxation process, particles can move widely within the time interval as short as a few free-fall times, because of the effective potential oscillations. Since such particle movement causes further potential oscillations, it is expected that the system approaches the critical state where such particle activities, which we call gravitational fugacity, is independent of the local position as much as possible. Here we demonstrate that gravitational fugacity can be described as the functional of the LV ratio, which means that the LV ratio is a key ingredient estimating the particle activities against gravitational potential. We also demonstrate that the LV relation is attained if the LV ratio exceeds the critical value b=1 everywhere in the bound region during the violent relaxation process. The local region which does not meet this criterion can be trapped into the presaturated state. However, small phase-space perturbation can bring the inactive part into the LV critical state.
authors.affiliation: Department of Physics, Ochanomizu University, 2-1-1 Ohtuka, Bunkyo, Tokyo 112-8610, Japan. sota@cosmos.phys.ocha.ac.jp
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Sota
authors.forename: Osamu
authors.initials: O
authors.lastname: Iguchi
authors.forename: Tohru
authors.initials: T
authors.lastname: Tashiro
authors.forename: Masahiro
authors.initials: M
authors.lastname: Morikawa