Abstract: Collisionless plasma shocks are a common feature of many space and astrophysical systems; from Earth’s bow shock to galaxy cluster mergers, collisionless shocks are sources of high-energy particles and non-thermal emission and can channel as much as 20% of the shock's energy into non-thermal particles. While the generation and acceleration of these non-thermal particles have been previously studied, how these particles feedback on the shock hydrodynamics has yet to be accurately detailed. In this colloquium, I will present recent results from self-consistent, hybrid particle-in-cell simulations that show the importance of self-generated, non-thermal particle populations on the nature of collisionless shocks. The energetic particles leak upstream of the shock and drive instabilities, which feedback on the shock dynamics. This collisionless process modifies the shock at zeroth order by increasing the compression ratio, slowing the shock, and altering the non-thermal population's energy distribution. These results can explain discrepancies between predictions and observations in a wide range of systems, such as inaccuracies of the predicted arrival times of coronal mass ejections, a dawn-dusk asymmetry of Earth’s bow shock, and conflicting radio and x-ray observations of intracluster shocks. These effects will likely need to be included in fluid modeling to predict shock evolution accurately.
Hosted by Professor Yi-Hsin Liu***Join before the Colloquium at 3:00 pm for coffee, cookies and brownies from Lou's in Wilder 103!***
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