New Insights on the Origin of Cosmic Rays

Abstract: The origin of the very energetic particles known as cosmic rays (CRs) has puzzled scientists for more than a century, since the pioneering discovery by Victor Hess in 1912. In the last decade, a new generation of X-ray and gamma-ray telescopes has been collecting evidence that CRs are accelerated up to about $10^8$ GeV in the blast waves of supernova remnants (SNRs). More recently, modern supercomputers have opened a new window on the processes responsible for particle acceleration in astrophysical collisionless plasmas, allowing the study of CR acceleration via first-principles kinetic simulations. I present the most recent results of large hybrid (kinetic ions – fluid electrons) simulations of non-relativistic shocks, in which ion acceleration efficiency and magnetic field amplification are investigated in detail as a function of shock inclination and strength. I also discuss the theoretical and observational counterparts of these findings, comparing them with predictions of diffusive shock acceleration theory and with observations of young SNRs. Finally, I present the first full kinetic simulations that also show efficient acceleration of electrons, which are crucial to understand the non-thermal emission from several astrophysical objects, such as SNRs, active galaxies, and galaxy clusters.