Collisionless Shocks in Active Galaxies and in a Laboratory Plasma

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In many astrophysical systems, a hot plasma forms a collisionless shock at the boundary with its environment, where, instead of collisions, turbulent interactions decelerate the faster plasma. Prominent examples are the bow shock of the Earth and most likely the jets of active galactic nuclei. For both cases, however, rigorous quantitative tests are needed to confirm widely discussed yet purely qualitative theories as to how these shocks may be formed. I will investigate the turbulence that facilitates the narrow transition between both sides of a collisionless shock from two perspectives, both numerically and experimentally.Starting with large numerical particle-in-cell simulations that I will run on computing clusters in Germany and the USA, I will calculate the scattering rates of charged particles in collisionless shocks with as yet unrivalled precision. These rates determine the highest energy that cosmic-ray particles in the jets of active galactic nuclei can achieve. A semianalytic model which has already been developed at the University of Würzburg will use these data to predict the variability of the radiation emitted by active galactic nuclei. Thus, we will be able to infer from measurements how much of the observed radiation is due to the acceleration of hadrons.Meanwhile, experiments with high-energy lasers in Los Angeles will produce the first parallel collisionless shocks in a laboratory plasma. Comparing the collected data with hybrid simulations, I will interpret the observations and contribute to optimising the experiment. We will be in a position to measure directly which instabilities are the most important in forming the shock. This insight will help us understand the role that plasma turbulence plays in the formation of planetary bow shocks.