The Quest for the Origins of Ultra-High-Energy Cosmic Rays

TL;DR

This paper reviews current theories and recent findings on the origins of ultra-high-energy cosmic rays, highlighting the challenges and future strategies for identifying their astrophysical sources.

Contribution

It provides a concise overview of acceleration theories, discusses recent observational results, and suggests strategies for advancing understanding of UHECR origins.

Findings

Reported excess of UHECRs around Centaurus A

Correlation of UHECRs with starburst galaxies

Joint modeling of spectrum, composition, and directions

Abstract

Significant progress has been made over the past decades towards unveiling the sources of the most energetic particles in nature, the ultra-high-energy cosmic rays (UHECRs). Despite these advancements, the exact astrophysical sites capable of accelerating these particles to such extreme energies remain largely unknown. Moreover, the mechanisms by which they achieve these extreme energies are poorly understood. Here, I provide a concise overview of the theory underlying the acceleration and propagation of UHECRs. I then critically discuss three recent results that could help unveil their origins: the reported excess around Centaurus A, the correlation with starburst galaxies, and the efforts to jointly model the energy spectrum, composition, and arrival directions. Finally, I discuss strategies for advancing this field, emphasising the need for refined theoretical models, the challenges in building them, and the potential for new observatories to shed light on the mysteries of UHECRs.