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Self-organized relaxation in a collisionless gravitating system.

Yasuhide Sota1, Osamu Iguchi, Tohru Tashiro

  • 1Department of Physics, Ochanomizu University, 2-1-1 Ohtuka, Bunkyo, Tokyo 112-8610, Japan. sota@cosmos.phys.ocha.ac.jp

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Summary

Collisionless self-gravitating systems reach equilibrium via self-organized relaxation. Gravitational fugacity, a measure of particle activity, becomes position-independent, indicating the system

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Area of Science:

  • Astrophysics
  • Statistical Mechanics
  • Plasma Physics

Background:

  • Collisionless self-gravitating systems exhibit complex dynamics during violent relaxation.
  • Understanding the approach to equilibrium in these systems is crucial for astrophysical modeling.
  • Previous models often simplified the particle dynamics and potential interactions.

Purpose of the Study:

  • To propose and analyze a self-organized relaxation process driving systems to equilibrium.
  • To define and investigate 'gravitational fugacity' as a measure of particle activity.
  • To establish the relationship between gravitational fugacity and the local virial (LV) ratio.

Main Methods:

  • Theoretical modeling of self-organized relaxation in collisionless self-gravitating systems.
  • Analysis of particle dynamics during violent relaxation, focusing on effective potential oscillations.
  • Mathematical description of gravitational fugacity as a functional of the LV ratio.

Main Results:

  • Demonstrated that gravitational fugacity becomes position-independent as systems approach equilibrium.
  • Established that the LV ratio is a key parameter for estimating particle activities against gravitational potential.
  • Showed that the local virial relation is achieved when the LV ratio exceeds a critical value of 1.

Conclusions:

  • The self-organized relaxation process leads to an equilibrium state defined by the local virial relation.
  • Gravitational fugacity provides a new metric to quantify particle activity and system relaxation.
  • Systems can be driven to the critical state even from a presaturated state via small perturbations.