Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Massive stars as major factories of Galactic cosmic rays

Nature Astronomy volume 3, pages 561–567 (2019)Cite this article

Subjects

This article has been updated

Abstract

The identification of the main contributors to the locally observed fluxes of cosmic rays is a prime objective in the resolution of the long-standing enigma of the source of cosmic rays. We report on a compelling similarity of the energy and radial distributions of multi-TeV cosmic rays extracted from observations of very-high-energy γ-rays towards the Galactic Centre and two prominent clusters of young massive stars, Cygnus OB2 and Westerlund 1. We interpret this resemblance as evidence that cosmic rays responsible for the diffuse very-high-energy γ-ray emission from the Galactic Centre are accelerated by the ultracompact stellar clusters located in the heart of the Galactic Centre. The derived 1/r decrement of the cosmic ray density with the distance from a star cluster is a distinct signature of continuous cosmic ray injection into the interstellar medium over a few million years. The lack of brightening of the γ-ray images towards the stellar clusters excludes the leptonic origin of γ-ray radiation. The hard, ∝E−2.3-type, power-law energy spectra of parent protons continues up to ~1 PeV. The efficiency of conversion of the kinetic energy of stellar winds to cosmic rays can be as high as 10%, implying that young massive stars may operate as proton PeVatrons with a dominant contribution to the flux of the highest-energy Galactic cosmic rays.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: γ-Ray luminosities and the radial distributions of CR protons in extended regions around the star clusters Cygnus OB2 (Cygnus Cocoon) and Westerlund 1 (Wd 1 Cocoon), as well as in the CMZ of the Galactic Centre assuming that the CMZ is powered by CRs accelerated in the Arches, Quintuplet and Nuclear clusters.

Similar content being viewed by others

Data availability

This paper makes use of Fermi LAT data, which can be downloaded from the Fermi LAT data server (https://fermi.gsfc.nasa.gov/ssc/data/access/), the H.E.S.S results used in this paper can be obtained from https://www.mpi-hd.mpg.de/hfm/HESS/pages/publications/auxiliary/AA537_A114.html for Westerlund 1 and https://www.mpi-hd.mpg.de/hfm/HESS/pages/publications/auxiliary/auxinfo_GalacticCenter.html for CMZ. The CO data used can be downloaded from the Radio Telescope Data Center (https://www.cfa.harvard.edu/rtdc/CO/). The HI data can be downloaded from http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/440/775. The Planck dust opacity map used can be downloaded from the Planck Legacy Archive (https://pla.esac.esa.int/#maps).

Change history

  • 24 April 2019

    In the version of this Article originally published, the following ‘Journal peer review information’ was missing: “Nature Astronomy thanks Don Ellison, Giovanni Morlino and the other anonymous reviewer(s) for their contribution to the peer review of this work.” This statement has now been added.

References

  1. Drury, L. O. Origin of cosmic rays. Astropart. Phys. 39-40, 52–60 (2012).

    Article  ADS  Google Scholar 

  2. Blasi, P. The origin of Galactic cosmic rays. Astron. Astrophys. Rev. 21, 70 (2013).

    Article  ADS  Google Scholar 

  3. Bell, A., Schure, K., Reville, B. & Giacinti, G. Cosmic ray acceleration and escape from supernova remnants. Mon. Not. R. Astron. Soc. 431, 415 (2013).

    Article  ADS  Google Scholar 

  4. Cardillo, M., Amato, E. & Blasi, P. On the cosmic ray spectrum from type II supernovae expanding in their red giant presupernova wind. Astropart. Phys. 69, 1 (2015).

    Article  ADS  Google Scholar 

  5. Zirakashvili, V. N. & Ptuskin, V. S. Type IIn supernovae as sources of high energy astrophysical neutrinos. Astropart. Phys. 78, 28 (2016).

    Article  ADS  Google Scholar 

  6. Borkowski, K. J. et al. Radioactive scandium in the youngest galactic supernova remnant G1.9 + 0.3. Astrophys. J. Lett. 724, L161 (2010).

    Article  ADS  Google Scholar 

  7. Aharonian, F., Sun, X.-n. & Yang, R.-z. Energy distribution of relativistic electrons in the young supernova remnant G1.9 + 0.3. Astron. Astrophys. 603, A7 (2017).

    Article  ADS  Google Scholar 

  8. Cristofari, P., Gabici, S., Terrier, R. & Humensky, T. B. On the search for Galactic supernova remnant PeVatrons with current TeV instruments. Mon. Not. R. Astron. Soc. 479, 3415 (2018).

    Article  ADS  Google Scholar 

  9. H.E.S.S. Collaboration TeV γ-ray observations of the young synchrotron-dominated SNRs G1.9 + 0.3 and G330.2 + 1.0 with H.E.S.S. Mon. Not. R. Astron. Soc. 441, 790 (2014).

  10. Kafexhiu, E., Aharonian, F., Taylor, A. M. & Vila, G. S. Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies. Phys. Rev. D 90, 123014 (2014).

    Article  ADS  Google Scholar 

  11. Casse, M. & Paul, J. A. Local gamma rays and cosmic-ray acceleration by supersonic stellar winds. Astrophys. J. 237, 236–243 (1980).

    Article  ADS  Google Scholar 

  12. Cesarsky, C. J. & Montmerle, T. Gamma rays from active regions in the galaxy—the possible contribution of stellar winds. Space Sci. Rev. 36, 173–193 (1983).

    Article  ADS  Google Scholar 

  13. Bykov, A. M. Nonthermal particles and photons in starburst regions and superbubbles. Astron. Astrophys. Rev. 22, 77 (2013).

    Article  ADS  Google Scholar 

  14. Parizot, E., Marcowith, A., van der Swaluw, E., Bykov, A. M. & Tatischeff, V. Superbubbles and energetic particles in the Galaxy. I. Collective effects of particle acceleration. Astron. Astrophys. 424, 747–760 (2004).

    Article  ADS  Google Scholar 

  15. Bykov, A. M. & Toptygin, I. N. Interstellar turbulence and the kinetics of cosmic rays. Akad. Nauk SSSR Izvestiia Seriia Fizicheskaia 46, 1659–1662 (1982).

    ADS  Google Scholar 

  16. Klepach, E. G., Ptuskin, V. S. & Zirakashvili, V. N. Cosmic ray acceleration by multiple spherical shocks. Astropart. Phys. 13, 161–172 (2000).

    Article  ADS  Google Scholar 

  17. Ackermann, M. et al. A cocoon of freshly accelerated cosmic rays detected by Fermi in the Cygnus superbubble. Science 334, 1103–1107 (2011).

    Article  ADS  Google Scholar 

  18. Yang, R.-z. & Aharonian, F. Diffuse γ-ray emission near the young massive cluster NGC 3603. Astron. Astrophys. 600, A107 (2017).

    Article  Google Scholar 

  19. Yang, R.-z., de Oña Wilhelmi, E. & Aharonian, F. Diffuse gamma-ray emission in the vicinity of young star cluster Westerlund 2. Astron. Astrophys. 611, A77 (2018).

    Article  Google Scholar 

  20. Aharonian, F., Buckley, J., Kifune, T. & Sinnis, G. High energy astrophysics with ground-based gamma ray detectors. Rep. Prog. Phys. 71, 096901 (2008).

    Article  ADS  Google Scholar 

  21. Abramowski, A. et al. Discovery of extended VHE γ-ray emission from the vicinity of the young massive stellar cluster Westerlund 1. Astron. Astrophys. 537, A114 (2012).

    Article  Google Scholar 

  22. Abramowski, A. et al. The exceptionally powerful TeV γ-ray emitters in the Large Magellanic Cloud. Science 347, 406–412 (2015).

    Article  ADS  Google Scholar 

  23. Bartoli, B. et al. Identification of the TeV gamma-ray source ARGO J2031 + 4157 with the Cygnus Cocoon. Astrophys. J. 790, 152 (2014).

    Article  ADS  Google Scholar 

  24. Aharonian, F. A. & Atoyan, A. M. On the emissivity of π0-decay gamma radiation in the vicinity of accelerators of Galactic cosmic rays. Astron. Astrophys. 309, 917–928 (1996).

    ADS  Google Scholar 

  25. Abramowski, A. et al. Acceleration of petaelectronvolt protons in the Galactic centre. Nature 531, 476–479 (2016).

    Article  ADS  Google Scholar 

  26. Kelner, S., Aharonian, F. A. & Bugayov, V. Energy spectra of gamma-rays, electrons and neutrinos produced at proton-proton interactions in the very high energy regime. Phys. Rev. D 74, 034018 (2006).

    Article  ADS  Google Scholar 

  27. Atoyan, A. M., Aharonian, F. A. & Völk, H. J. Electrons and positrons in the Galactic cosmic rays. Phys. Rev. D 52, 3265–3275 (1995).

    Article  ADS  Google Scholar 

  28. Strong, A. W., Moskalenko, I. V. & Ptuskin, V. S. Cosmic-ray propagation and interactions in the Galaxy. Annu. Rev. Nuc. Part. Sci. 57, 285–327 (2007).

    Article  ADS  Google Scholar 

  29. Actis, M. et al. Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy. Exp. Astron. 32, 193 (2011).

    Article  ADS  Google Scholar 

  30. Bykov, A. M., Ellison, D. C., Gladilin, P. E. & Osipov, S. M. Ultrahard spectra of PeV neutrinos from supernovae in compact star clusters. Mon. Not. R. Astron. Soc. 453, 113–121 (2015).

    Article  ADS  Google Scholar 

  31. Aguilar, M. et al. Precision measurement of the proton flux in primary cosmic rays from rigidity 1 GV to 1.8 TV with the Alpha Magnetic Spectrometer on the International Space Station. Phys. Rev. Lett. 114, 171103 (2015).

    Article  ADS  Google Scholar 

  32. Ellison, D. C., Drury, L. O. & Meyer, J.-P. Galactic cosmic rays from supernova remnants. II. Shock acceleration of gas and dust. Astrophys. J. 487, 197 (1997).

    Article  ADS  Google Scholar 

  33. Binns, W. R. et al. Observation of the 60Fe nucleosynthesis-clock isotope in Galactic cosmic rays. Science 352, 677–680 (2016).

    Article  ADS  Google Scholar 

  34. The Fermi-LAT Collaboration. Fermi Large Area Telescope third source catalog. Astrophys. J. Suppl. 218, 23 (2015).

    Article  ADS  Google Scholar 

  35. Abdo, A. A. et al. Spectrum and morphology of the two brightest Milagro sources in the Cygnus region: MGRO J2019 + 37 and MGRO J2031 + 41. Astrophys. J. 753, 159 (2012).

    Article  ADS  Google Scholar 

  36. Mirzoyan, R. & Mukherjee, R. TeV gamma-ray emission from PSR J2032 + 4127/ MT91 213 at periastron. Astronomer’s Telegram 10971 (2017).

  37. Dermer, C. D. Secondary production of neutral pi-mesons and the diffuse Galactic gamma radiation. Astron. Astrophys. 157, 223–229 (1986).

    ADS  Google Scholar 

  38. Mori, M. Nuclear enhancement factor in calculation of Galactic diffuse gamma-rays: a new estimate with DPMJET-3. Astropart. Phys. 31, 341–343 (2009).

    Article  ADS  Google Scholar 

  39. Figer, D. F. Young massive clusters. In Proc. IAU Symp.Massive Stars as Cosmic Engines (eds Bresolin, F. et al.) Vol. 250, 247–256 (2008).

    Article  Google Scholar 

  40. Muno, M. P. et al. Diffuse, nonthermal X-ray emission from the Galactic star cluster Westerlund 1. Astrophys. J. 650, 203–211 (2006).

    Article  ADS  Google Scholar 

  41. Hußmann, B. The Quintuplet Cluster—A Young Massive Cluster Study Based on Proper Motion Membership. PhD thesis, Universität Bonn (2014).

Download references

Author information

Author notes

  1. These authors contributed equally: Felix Aharonian, Ruizhi Yang, Emma de Oña Wilhelmi.

Authors and Affiliations

  1. Dublin Institute for Advanced Studies, Dublin, Ireland

    Felix Aharonian

  2. Max-Planck-Institut für Kernphysik, Heidelberg, Germany

    Felix Aharonian & Ruizhi Yang

  3. Gran Sasso Science Institute, L’Aquila, Italy

    Felix Aharonian

  4. Institute of Space Sciences (ICE/CSIC), Barcelona, Spain

    Emma de Oña Wilhelmi

  5. Institut d’ Estudis Espacials de Catalunya (IEEC), Barcelona, Spain

    Emma de Oña Wilhelmi

  6. Deutsches Elektronen Synchrotron DESY, Zeuthen, Germany

    Emma de Oña Wilhelmi

Authors
  1. Felix Aharonian
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Ruizhi Yang
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Emma de Oña Wilhelmi
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

R.Y. and E.d.O.W. performed the data analysis and helped with writing the manuscript. F.A. was responsible for the interpretation of the data and led the writing of the manuscript.

Corresponding author

Correspondence to Ruizhi Yang.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Journal peer review information: Nature Astronomy thanks Don Ellison, Giovanni Morlino and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary text, Supplementary Figures 1–11, Supplementary Tables 1–2, Supplementary references.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Aharonian, F., Yang, R. & de Oña Wilhelmi, E. Massive stars as major factories of Galactic cosmic rays. Nat Astron 3, 561–567 (2019). https://doi.org/10.1038/s41550-019-0724-0

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41550-019-0724-0

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing