Wave instabilities in AGN jets

Supermassive black holes in active galactic nuclei (AGN) are known to launch relativistic jets, which are observed across the entire electromagnetic spectrum and are commonly thought to be the accelerators of ultra-high energy cosmic rays. Their primary radiation mechanism is synchrotron emission produced by a population of non-thermal electrons. The way these jets accelerate the electrons and ions is still a matter of active debate. In my talk, I will show that the shear layer between the jet and the ambient wind can be unstable to waves. As the waves fold magnetic field lines, they trigger magnetic reconnection and induce turbulence along the jet-wind interface. Additionally, the waves mix the mater-dominated wind with the electromagnetically dominated jet, mass loading the jet with ions. Therefore, this shear layer may be a site for particle energization, potentially explaining both the non-thermal nature of the electrons and the origin of ultra-high energy cosmic rays. To confirm that these waves are present in AGN, we propose to look for distinct features in polarization signatures that will be resolvable by next-generation global mm-VLBI facilities.