Oct 21, 2020

Speaker: James Binney (Rudolf Peierls Centre for Theoretical Physics, Oxford University)

Title: A revolution in relaxation

Abstract: There's a standard theory of how star clusters relax that has been taught for

decades. But is it correct? It's based on the idea that mutual attraction

causes stars to scatter off each other. Developments since 2010 suggest that

this picture is hopelessly naive because it neglects (a) the cluster's

self-gravity, and (b) the importance of resonant interactions in perturbative

problems.

I'll introduce the Balescu-Lenard equation, which predicts how systems relax.

After outlining how this equation explains why discs evolve so rapidly

through spiral structure, I'll discuss the application of the BL eqn to

clusters. N-body simulations suggest that the BL equation describes

relaxation much better than does classical theory. Looking ahead,

satisfactory application of the BL eqn to clusters requires a better

understanding of thermal fluctuations in clusters, and in of the Landau and

van Kampen modes of clusters.