Particle Acceleration in Highly Magnetized Plasmas with Luca Comisso

Turbulence and magnetic reconnection are ubiquitous in astrophysical environments and are often invoked to explain the origin of non-thermal particles inferred to be accelerated in a variety of astrophysical sources. However, the mechanisms responsible for accelerating particles to ultra-relativistic energies remain poorly understood. In this talk, I will present recent insights from first-principles particle-in-cell (PIC) simulations that, thanks to significant computational advances, have successfully bridged the gap between microscopic/kinetic scales and macroscopic/MHD scales, enabling the direct application of first-principles results to astrophysical systems. In particular, I will revisit our understanding of particle acceleration in magnetic reconnection layers, which have now been shown to produce broken power-law distributions in particle energy, along with pitch-angle anisotropy. Additionally, I will present results from unprecedentedly large-scale PIC simulations of magnetized turbulence, highlighting the role of reconnection in turbulence and stochastic particle acceleration in large-scale turbulence fluctuations. I will discuss the implications of reconnection-generated anisotropic pitch-angle distributions in astrophysical plasmas. If time permits, I will also discuss how some of these insights relate to the acceleration of ultrahigh-energy cosmic rays, the most energetic particles to reach Earth, in light of the Pierre Auger Observatory’s spectrum and composition measurements.

Sponsored by the McDonnell Center for the Space Sciences.