Collisionless relaxation in gravitational systems: From violent relaxation to gravothermal collapse

Abstract

Theory and simulations are used to study collisionless relaxation of a gravitational N -body system. It is shown that when the initial one-particle distribution function satisfies the virial condition--potential energy is minus twice the kinetic energy--the system quickly relaxes to a metastable state described quantitatively by the Lynden-Bell distribution with a cutoff. If the initial distribution function does not meet the virial requirement, the system undergoes violent oscillations, resulting in a partial evaporation of mass. The leftover particles phase-separate into a core-halo structure. The theory presented allows us to quantitatively predict the amount and the distribution of mass left in the central core, without any adjustable parameters. On a longer time scale tauG-N , collisionless relaxation leads to a gravothermal collapse.

Breathing Fire: How Stellar Feedback Drives Radial Migration, Rapid Size Fluctuations, and Population Gradients in Low-Mass Galaxies

“…(effectively) collisionless fluids, so that a time-varying gravitational potential will transfer energy to both species, regardless of particle mass (Lynden-Bell 1967;Henriksen & Widrow 1997;Levin et al 2008). Across a wide range of galaxy M star , the scale lengths of observed and simulated stellar density profiles are approximately equal to the characteristic sizes of galaxies' dark matter cores (Gentile et al 2009;Governato et al 2010;Brooks et al 2011).…”

Kinetic theory of spatially inhomogeneous stellar systems without collective effects

“…Numerical simulations starting from homogeneous spheres (see e.g. Roy & Perez 2004;Levin et al 2008;Joyce et al 2009) show little angular momentum mixing and lead to different results. In particular, they display a larger amount of mass loss (evaporation) than simulations starting from clumpy initial conditions.…”

“…Understanding the origin of incomplete relaxation, and developing models of incomplete violent relaxation to predict the structure of galaxies, is a very difficult problem (Arad & Johansson 2005). Some models of incomplete violent relaxation have been proposed based on different physical arguments (Bertin & Stiavelli 1984;Stiavelli & Bertin 1987;Hjorth & Madsen 1991;Chavanis et al 1996;Chavanis 1998;Levin et al 2008).…”

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