On particle acceleration and transport in plasmas in the Galaxy: theory and observations

TL;DR

This paper reviews recent observational data and theoretical models concerning the origin and propagation of Galactic Cosmic Rays, highlighting new findings, challenges to existing theories, and the need for paradigm shifts in understanding cosmic ray sources.

Contribution

It provides a comprehensive synthesis of recent observations and theoretical developments in Galactic Cosmic Ray research, emphasizing areas where current models are challenged or need refinement.

Findings

Confirmation of existing theories about cosmic ray acceleration and propagation.

Identification of unexpected features in cosmic ray spectra requiring new explanations.

Evidence suggesting possible paradigm shifts in understanding cosmic ray origins.

Abstract

Accelerated particles are ubiquitous in the Cosmos and play a fundamental role in many processes governing the evolution of the Universe at all scales, from the sub-AU ones relevant for the formation and evolution of stars and planets to the Mpc ones involved in Galaxy assembly. We reveal the presence of energetic particles in many classes of astrophysical sources thanks to their production of non-thermal radiation, and we detect them directly at Earth as Cosmic Rays. In the last two decades both direct and indirect observations have provided us a wealth of new, high quality data about Cosmic Rays and their interactions both in sources and during propagation, in the Galaxy and in the solar system. Some of the new data have confirmed existing theories about particle acceleration and propagation and their interplay with the environment in which they occur. Some others have brought about interesting surprises, whose interpretation is not straightforward within the standard framework and may require a change of paradigm in terms of our ideas about the origin of cosmic rays of different species or in different energy ranges. In this article, we will focus on Cosmic Rays of galactic origin, namely with energies below a few PeV, where a steepening is observed in the spectrum of energetic particles detected at the Earth. We review the recent observational findings and the current status of the theory about the origin and propagation of Galactic Cosmic Rays.