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The contribution of winds from star clusters to the Galactic cosmic-ray population

Nature Astronomy volume 8, pages 530–537 (2024)Cite this article

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Abstract

Cosmic rays (CR) are energetic nuclei that permeate the entire Galactic disk. Their existence requires the presence of powerful particle accelerators. While Galactic supernova explosions may supply the required energy, there is growing evidence that they cannot explain all of the observed properties of cosmic rays, such as their maximum particle energy and isotopic composition. Among Galactic objects, winds from stellar clusters meet the energetic requirement and provide a suitable environment for particle acceleration. The recent detection of some of these objects in γ rays confirms that they indeed harbour high-energy particles. However, as most supernovae explode inside stellar clusters, it is difficult to distinguish the contribution of winds to particle acceleration. Here we report the detection of young star clusters in the nearby Vela molecular ridge star-forming region. The young age of the systems guarantees an unbiased estimate of the stellar CR luminosity free from any supernova or pulsar contamination and allows us to draw conclusions on the acceleration efficiency and the total power supplied by these objects. We demonstrate that much more than 1% of the wind mechanical power is converted into CRs and consequently conclude that a small but non-negligible fraction, ~1–10% of the CR population, is contributed by stellar clusters.

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Fig. 1: Test statistic map of the analysed sources.
Fig. 2: Spectral energy distributions of the targeted star clusters.

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Data availability

The authors made use of publicly available data that can be retrieved at https://fermi.gsfc.nasa.gov/cgi-bin/ssc/LAT/LATDataQuery.cgi. Other data related to this work can be found on figshare: https://doi.org/10.6084/m9.figshare.24467155. Source data are provided with this paper.

Code availability

The authors made use of publicly available analysis software. In particular: fermipy v.1.0.2 available at https://github.com/fermiPy/fermipy/blob/master/docs/index.rst and naima available at https://github.com/zblz/naima.

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Acknowledgements

We would like to acknowledge J. Hinton, E. Amato, G. Morlino, R. Tuffs and M. Lemoine-Goumard for the suggestions and discussion. G.P. and S.G. are supported by Agence Nationale de la Recherche (grant ANR-21-CE31-0028). S.C. acknowledges support from the Polish Science Centre grant DEC-2017/27/B/ST9/02272.

Author information

Authors and Affiliations

  1. Université de Paris, CNRS, Astroparticule et Cosmologie, Paris, France

    Giada Peron & Stefano Gabici

  2. Max Planck Institute für Kernphysik, Heidelberg, Germany

    Giada Peron & Felix Aharonian

  3. Institute of Nuclear Physics, Krakow, Poland

    Sabrina Casanova

  4. Lehrstuhl für Astronomie, Universität Würzburg, Würzburg, Germany

    Vardan Baghmanyan

  5. Dublin Institute for Advanced Studies, Dublin, Ireland

    Felix Aharonian

  6. Yerevan State University, Yerevan, Armenia

    Felix Aharonian

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Contributions

G.P. led the data analysis, proposed the interpretation and produced the manuscript and its figures. S.C. proposed the target region as a case study. V.B. cross-checked the Fermi-LAT analysis. G.P., S.G., S.C. and F.A. gave significant inputs on data interpretation. All authors participated in the discussions and editing of the paper.

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Correspondence to Giada Peron.

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Supplementary Figs. 1–3.

Source data

Source Data Fig. 1

Spectral points. This data file contains the spectral energy distributions of the clusters discussed in the paper.

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Peron, G., Casanova, S., Gabici, S. et al. The contribution of winds from star clusters to the Galactic cosmic-ray population. Nat Astron 8, 530–537 (2024). https://doi.org/10.1038/s41550-023-02168-6

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