Unravelling the dynamics of cosmic vortices: Probing a Kelvin-Helmholtz instability in the jet of 3C 84

Abstract: Understanding the creation of relativistic jets originating from active galactic nuclei, require a thorough understanding of the accompanying plasma instabilities. Our high sensitivity, high resolution, global very long baseline interferometry observations of the jet in the radio galaxy 3C 84 enable us to study its inner morphology, which resembles a thread-like pattern. We find that this pattern can be described by a Kelvin-Helmholtz instability, consisting of four instability modes. Our model favours a jet described by a Mach number of $M_\textrm{j} = 5.0\pm1.7$ and a sound speed of $\alpha_\textrm{j} = 0.14\pm0.06$. With it, we are able to describe the internal structure of 3C 84 and to tentatively connect the origin of the instability to accretion disc activity.