Institute for Advanced Study Astrophysics Seminar

Classical stellar dynamics was largely concerned with equilibrium configurations of galaxies and star clusters. We are now able to resolve fine details and need to be able to model fluctuations around equilibria - moreover, it's long been recognised that fluctuations drive secular evolution. In any other branch of physics we analyse fluctuations through normal modes. When stellar dynamicists speak of 'modes' they are not referring to normal modes but objects identified by Landau that lack essential features of normal modes - e.g., completeness and additive energies.  The normal modes of collisionless systems were identified by van Kampen but have been largely ignored. I'll explain what these modes are mathematically and physically, explain their properties, how they relate to Landau's objects and how their properties enable us to understand the characteristic dissipative behaviour of stellar systems and the impact that Poisson noise has in them.