The hunt of PeVatrons as the origin of the most energetic photons observed in our Galaxy

TL;DR

This paper reviews the current understanding of PeVatrons, the astrophysical sources capable of accelerating particles to petaelectronvolt energies, discussing theoretical conditions, potential sources, recent experimental findings, and future prospects.

Contribution

It provides a comprehensive overview of the theoretical criteria and candidate sources for Galactic PeVatrons, integrating recent experimental data and outlining future research directions.

Findings

Identification of potential Galactic PeVatrons based on recent observations

Summary of theoretical conditions necessary for plasma acceleration to PeV energies

Discussion of experimental evidence supporting the existence of PeVatrons

Abstract

Ultrarelativistic particles called cosmic rays permeate the Milky Way, propagating through the Galactic turbulent magnetic fields. The mechanisms under which these particles increase their energy can be reasonably described by current theories of acceleration and propagation of cosmic rays. There are, however, still many open questions as to how to reach petaelectronvolt (PeV) energies, the maximum energy believed to be attained in our Galaxy, and in which astrophysical sources (dubbed {\it PeVatrons}) this ultra-high energy acceleration happens. In this article, we describe the theoretical conditions for plasma acceleration to these energies, and the Galactic sources in which these conditions are possible. These theoretical predictions are then confronted with the latest experimental results, summarising the state-of-the-art of our current knowledge of PeVatrons. We finally describe the prospects to keep advancing the understanding of these elusive objects, still unidentified more than one hundred years after the discovery of cosmic rays.