Experimental observation of violent relaxation in a non-linear optical system

Martino Lovisetto

The process of self-gravitating collapse and the subsequent formation of galaxies and globular clusters, via the so-called violent relaxation mechanism, is still not well understood. Moreover, astrophysical time-scales are so large that it is not possible to directly observe this dynamics; for this reason, it is useful to perform experiments in analogue systems. In this work, we present the results of an experiment in a nonlinear optical medium with long-range thermal nonlocal nonlinearity, which is analogue to a self-gravitating system described by the Newton-Schrödinger Equation (NSE), where quantum effects arise to macroscopic galactic scales. We explain how to control experimentally the analogue of $\hbar\m$ and compare quantitatively the theoretical concepts and the experimental aspects. We observe some characteristic features of the formation of an analogue galaxy through the process of violent relaxation, such as mixing, filamentation of phase space, and Landau damping.