NAM 2021 Session – From Plasma to Galactic Dynamics: Collisionless Physics Across the Universe

April 7, 2021, from Oliver Allanson, Thomas Neukirch, Chris Hamilton, Luca Franci, Jean-Baptiste Fouvry

We invite abstract submissions for a session ‘From Plasma to Galactic Dynamics: Collisionless Physics Across the Universe’ at the VIRTUAL UK National Astronomy Meeting, 19th-23rd July, 2021,

We would also like to highlight that there are a significant number of other GEM/solar/magnetospheric/space weather/space plasma physics related sessions at NAM 2021,

Abstract deadline is Friday 30th April 2021 at 1700 UTC. Full details can be found at

Invited speakers: David Burgess (Queen Mary University of London) & Benoit Famaey (Observatoire astronomique de Strasbourg).

The dynamics of many physical systems across the Universe are well described using the collisionless approximation: for which the mean free path is significantly larger than the most important length scales. In these cases, the statistical evolution of many bodies is determined by the collisionless Boltzmann (aka the Vlasov) equation. From the Earth’s radiation belts, through the magnetosphere, solar wind, interstellar medium and beyond to even more exotic relativistic and high-energy astrophysical environments, charged particle dynamics are commonly collisionless. One of the most important implications of low collisionality is the departure of particle distributions from thermal equilibrium. This, and other effects, play a vital role in diverse plasma physics phenomena such as wave-particle interactions, magnetic reconnection, collisionless shocks, cross-scale coupling and turbulence. Furthermore, the evolution of galaxies themselves is often treated as a collisionless process, with galactic dynamics and other self-gravitating systems also modelled using Vlasov theory. One important and common theme that unites these seemingly disparate plasma and gravitational applications is the fact that in the absence of collisions/thermalisation, nature needs to find another route to dissipate energy. Kinetic plasma instabilities are one such route; and in disk galaxies, the Landau damping of density waves on resonantly orbiting stars is thought responsible for the ‘heating’ of the stellar velocity distribution. Modern satellites such as MMS, Parker Solar Probe and Solar Orbiter are revealing the true kinetic nature of plasma within our solar system. Analogously, the Gaia satellite is revealing signatures of these kinetic effects in the Milky Way. Furthermore, increasing computational power is making more ambitious kinetic and hybrid numerical experiments a reality (e.g. the system-scale kinetic modelling undertaken by the Vlasiator group). In astrophysics, N-body simulations are becoming so efficient that direct comparison with the kinetic theory is achievable. In this inter-disciplinary session we welcome all observational, theoretical and modelling work that considers the physics of collisionless systems – in either (or both of) the plasma and gravitational contexts.