Abstract
Ultrarelativistic particles called cosmic rays permeate the Milky Way, propagating through the turbulent Galactic 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 PeVatrons) this ultrahigh-energy acceleration happens. In this Review, 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 compared to the latest experimental results, summarizing 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 100 years after the discovery of cosmic rays.
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Acknowledgements
This article is the result of fruitful discussions during the 2nd HONEST (Hot Topics in High Energy Astrophysics) Workshop ‘PeVatrons and their environments’ (see https://indico.desy.de/event/34265/). We thank the scientific organizing committee of the workshop, composed of the authors of this Review, plus T. Bell (University of Oxford), D. Berge (DESY Zeuthen), J. Cortina (CIEMAT), P. Huentemeyer (Michigan Tech University), S. Recchia (INFN Torino) and R. Zanin (CTA Observatory); the Local Organizing Committee, J. Eckert, S. Patel, J. Kramer and M. I. Bernardos; and all the participants of the workshop, without whom the fruitful discussions would not have been possible. R.L.-C. acknowledges the Ramón y Cajal programme through grant RYC-2020-028639-I. R.L.-C. also acknowledges financial support from the Spanish ‘Ministerio de Ciencia e Innovación’ (MCIN/AEI/ 10.13039/501100011033) through the Center of Excellence Severo Ochoa award for the Instituto de Astrofísica de Andalucía-CSIC (CEX2021-001131-S), and through grants PID2019-107847RB-C44 and PID2022-139117NB-C44. E.A. acknowledges support by INAF under grant PRIN-INAF 2019, and by the European Union - Next Generation EU through grant PRIN-MUR 2022TJW4EJ. S.G. acknowledges support from Agence Nationale de la Recherche (project CRitiLISM, ANR-21-CE31-0028).
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de Oña Wilhelmi, E., López-Coto, R., Aharonian, F. et al. The hunt for PeVatrons as the origin of the most energetic photons observed in the Galaxy. Nat Astron 8, 425–431 (2024). https://doi.org/10.1038/s41550-024-02224-9
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DOI: https://doi.org/10.1038/s41550-024-02224-9