Active Galactic Nuclei: Sources for ultra high energy cosmic rays?

TL;DR

This paper reviews the current understanding of ultra high energy cosmic rays, emphasizing the potential sources like radio galaxies and gamma ray bursts, and discusses the challenges posed by magnetic fields and limited data.

Contribution

It provides a comprehensive overview of the current state of research on the origins of ultra high energy cosmic rays and outlines future directions for progress.

Findings

Radio galaxies are favored as potential sources.

Magnetic fields significantly influence cosmic ray propagation.

Current data is insufficient for definitive conclusions.

Abstract

The origin of ultra high energy cosmic rays promises to lead us to a deeper understanding of the structure of matter. This is possible through the study of particle collisions at center-of-mass energies in interactions far larger than anything possible with the Large Hadron Collider, albeit at the substantial cost of no control over the sources and interaction sites. For the extreme energies we have to identify and understand the sources first, before trying to use them as physics laboratories. Here we describe the current stage of this exploration. The most promising contenders as sources are radio galaxies and gamma ray bursts. The sky distribution of observed events yields a hint favoring radio galaxies. Key in this quest are the intergalactic and galactic magnetic fields, whose strength and structure are not yet fully understood. Current data and statistics do not yet allow a final judgment. We outline how we may progress in the near future.