The great similarity between plasmas and galaxies, part 2: spiral waves from an instability of 2D BGK modes

In a Journal Club talk last fall (2022), I talked about a great similarity between the kinetic description of plasmas and stellar systems such as galaxies, based on two of my recent results: a linear problem on Landau damping in stellar systems [Astrophys. J., 923, 271 (2021)], and a new three-dimensional (3D) “Galactic Disk”-model of a nonlinear equilibrium in plasmas known as a Bernstein-Greene-Kruskal (BGK) mode [arxiv: 2207.11632 (2022)]. Towards the end of that talk, I briefly mentioned a third preliminary result to compare with spiral structures of galaxies. Since then, we have confirmed with more Particle-in-Cell (PIC) simulations of the excitation of spiral waves when a 2D BGK mode becomes unstable. I will talk about these simulations, as well as a new local stability analysis to try to understand these results.