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:

Effective shielding of ≲10 GeV cosmic rays from dense molecular clumps

Nature Astronomy volume 7, pages 351–358 (2023)Cite this article

Subjects

Abstract

The density of cosmic rays inside molecular clouds determines the ionization rate in the dense cores where stars form. It is also one of the drivers of astrochemistry leading to the creation of complex molecules. Through Fermi Large Area Telescope observations of nearby giant molecular clouds, we observed deficits (holes) in the gamma-ray residual map when modelling with the expected gamma-ray diffuse emission from uniform cosmic rays interacting with the molecular content. We propose that the deficit is due to the lack of penetration of the low-energy (sub-GeV to GeV) cosmic rays into denser regions or clumps. This differs from the prevailing view of fast cosmic ray transport in giant molecular clouds where the magnetic turbulence is suppressed by neutral-ion damping, as our results require a slow diffusion inside dense molecular clumps. Through modelling we find that while the shielding is negligible on the cloud scale, it becomes important in the denser, parsec-sized regions where the gravitational collapse is already at play, changing the initial condition of star formation and astrochemistry.

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: The total column density derived from the Planck dust-opacity map.
Fig. 2: The gamma-ray spectra obtained from Fermi-LAT observations and the derived CR energy density.
Fig. 3: Shielding effect toward structures of different masses and sizes.

Similar content being viewed by others

Data availability

The Fermi-LAT data used in this work is provided online by the NASA-GSFC Fermi Science Support Center, and can be downloaded from the data server at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/. The Planck dust-opacity map is publicly available in the Planck Legacy Archive (http://pla.esac.esa.int/pla/aio/product-action?MAP.MAP_ID=COM_CompMap_ThermalDust-commander_2048_R2.00.fits).

Code availability

Fermi-LAT data used in our study were reduced and analysed using the standard FERMITOOLS v.1.0.1 software package available from https://github.com/fermi-lat/Fermitools-conda/wiki.

References

  1. Aharonian, F., Yang, R. & de Oña Wilhelmi, E. Massive stars as major factories of Galactic cosmic rays. Nat. Astron. 3, 561–567 (2019).

    Article  ADS  Google Scholar 

  2. Dalgarno, A. The Galactic cosmic ray ionization rate. Proc. Natl Acad. Sci. USA 103, 12269–12273 (2006).

    Article  ADS  Google Scholar 

  3. Papadopoulos, P. P. A cosmic-ray-dominated interstellar medium in ultra luminous infrared galaxies: new initial conditions for star formation. Astrophys. J. 720, 226–232 (2010).

    Article  ADS  Google Scholar 

  4. Aharonian, F. A. Gamma rays from molecular clouds. Space Sci. Rev. 99, 187–196 (2001).

    Article  ADS  Google Scholar 

  5. Kainulainen, J., Beuther, H., Henning, T. & Plume, R. Probing the evolution of molecular cloud structure. From quiescence to birth. Astron. Astrophys. 508, L35–L38 (2009).

    Article  ADS  Google Scholar 

  6. Chen, B. Q. et al. A large catalogue of molecular clouds with accurate distances within 4 kpc of the Galactic disc. Mon. Not. R. Astron. Soc. 493, 351–361 (2020).

    Article  ADS  Google Scholar 

  7. Lada, C. J. & Dame, T. M. The mass–size relation and the constancy of GMC surface densities in the Milky Way. Astrophys. J. 898, 3 (2020).

    Article  ADS  Google Scholar 

  8. Williams, J. P., Blitz, L. & McKee, C. F. The Structure and Evolution of Molecular Clouds:from Clumps to Cores to the IMF. in Mannings, V., Boss, A.P., Russell, S. S. (eds.) Protostars and Planets IV, Tucson: University of Arizona Press, 97-121 (2000)

  9. Dobbs, C. L., Burkert, A. & Pringle, J. E. Why are most molecular clouds not gravitationally bound? Mon. Not. R. Astron. Soc. 413, 2935–2942 (2011).

    Article  ADS  Google Scholar 

  10. Pfalzner, S. et al. Observational constraints on star cluster formation theory. I. The mass–radius relation. Astron. Astrophys. 586, A68 (2016).

    Article  Google Scholar 

  11. Li, G.-X. Criteria for gravitational instability and quasi-isolated gravitational collapse in turbulent medium. Mon. Not. R. Astron. Soc. 465, 667–671 (2017).

    Article  ADS  Google Scholar 

  12. Cesarsky, C. J. & Volk, H. J. Cosmic ray penetration into molecular clouds. Astron. Astrophys. 70, 367-377 (1978).

  13. Crutcher, R. M. Magnetic fields in molecular clouds. Annu. Rev. Astron. Astrophys. 50, 29–63 (2012).

    Article  ADS  Google Scholar 

  14. Kritsuk, A. G., Norman, M. L., Padoan, P. & Wagner, R. The statistics of supersonic isothermal turbulence. Astrophys. J. 665, 416–431 (2007).

    Article  ADS  Google Scholar 

  15. Li, G.-X. Scale-free gravitational collapse as the origin of ρ ~ r−2 density profile—a possible role of turbulence in regulating gravitational collapse. Mon. Not. R. Astron. Soc. 477, 4951–4956 (2018).

    Article  ADS  Google Scholar 

  16. Donkov, S. & Stefanov, I. Z. Density distribution function of a self-gravitating isothermal compressible turbulent fluid in the context of molecular clouds ensembles. Mon. Not. R. Astron. Soc. 474, 5588–5597 (2018).

    Article  ADS  Google Scholar 

  17. Ungerechts, H. & Thaddeus, P. A CO survey of the dark nebulae in Perseus, Taurus, and Auriga. Astrophys. J. Suppl. Ser. 63, 645 (1987).

    Article  ADS  Google Scholar 

  18. Dame, T. M., Hartmann, D. & Thaddeus, P. The Milky Way in molecular clouds: a new complete CO survey. Astrophys. J. 547, 792–813 (2001).

    Article  ADS  Google Scholar 

  19. Walter, F. M. & Boyd, W. T. Star formation in Taurus–Auriga: the high-mass stars. Astrophys. J. 370, 318-323 (1991).

  20. Yang, Rui-zhi, de Oña Wilhelmi, E. & Aharonian, F. Probing cosmic rays in nearby giant molecular clouds with the Fermi Large Area Telescope. Astron. Astrophys. 566, A142 (2014).

    Article  Google Scholar 

  21. Planck Collaboration et al. Planck 2013 results. XI. All-sky model of thermal dust emission. Astron. Astrophys. 571, A11 (2014).

    Article  Google Scholar 

  22. Abdollahi, S. et al. Fermi Large Area Telescope fourth source catalog. Astrophys. J. Suppl. Ser. 247, 33 (2020).

    Article  ADS  Google Scholar 

  23. Liseau, R. et al. Gas and dust in the star-forming region ρ Oph A. The dust opacity exponent β and the gas-to-dust mass ratio g2d. Astron. Astrophys. 578, A131 (2015).

    Article  Google Scholar 

  24. Huang, X., Yuan, Q. & Fan, Y.-Z. A GeV–TeV particle component and the barrier of cosmic-ray sea in the Central Molecular Zone. Nat. Commun. 12, 6169 (2021).

    Article  ADS  Google Scholar 

  25. Mercimek, S., Myers, P. C., Lee, K. I. & Sadavoy, S. I. An estimation of the star formation rate in the Perseus Complex. Astron. J. 153, 214 (2017).

    Article  ADS  Google Scholar 

  26. Arce, H. G. et al. Molecular Outflows in Low- and High-Mass Star-forming Regions. InReipurth, B., Jewitt, D. & Keil, K. (eds.) Protostars and Planets V, Tucson: University of Arizona Press, 245-260 (2007)

  27. Owen, E. R., On, A. Y. L., Lai, S.-P. & Wu, K. Observational signatures of cosmic-ray interactions in molecular clouds. Astrophys. J. 913, 52 (2021).

    Article  ADS  Google Scholar 

  28. Gabici, S., Aharonian, F. A. & Blasi, P. Gamma rays from molecular clouds. Astrophys. Space Sci. 309, 365–371 (2007).

    Article  ADS  Google Scholar 

  29. Veltchev, T. V., Donkov, S. & Klessen, R. S. Modelling the structure of molecular clouds. I. A multiscale energy equipartition. Mon. Not. R. Astron. Soc. 459, 2432–2443 (2016).

    Article  ADS  Google Scholar 

  30. Li, G.-X. & Burkert, A. Probing the multiscale interplay between gravity and turbulence—power-law-like gravitational energy spectra of the Orion Complex. Mon. Not. R. Astron. Soc. 464, 4096–4106 (2017).

    Article  ADS  Google Scholar 

  31. Li, G.-X. & Burkert, A. Quantifying the interplay between gravity and magnetic field in molecular clouds—a possible multiscale energy equipartition in NGC 6334. Mon. Not. R. Astron. Soc. 474, 2167–2172 (2018).

    Article  ADS  Google Scholar 

  32. Berezinskii, V. S., Bulanov, S. V., Dogiel, V. A. & Ptuskin, V. S. Astrophysics of Cosmic Rays (North–Holland, 1990).

  33. Morlino, G. & Gabici, S. Cosmic ray penetration in diffuse clouds. Mon. Not. R. Astron. Soc. 451, L100–L104 (2015).

    Article  ADS  Google Scholar 

  34. Crutcher, R. M. Magnetic fields in molecular clouds. Annu. Rev. Astron. Astrophys. 50, 29–63 (2012).

    Article  ADS  Google Scholar 

  35. Dogiel, V. A. et al. Gamma-ray emission from molecular clouds generated by penetrating cosmic rays. Astrophys. J. 868, 114 (2018).

    Article  ADS  Google Scholar 

  36. Jiang, B. et al. Cavity of molecular gas associated with supernova remnant 3C 397. Astrophys. J. 712, 1147–1156 (2010).

    Article  ADS  Google Scholar 

  37. Casse, F., Lemoine, M. & Pelletier, G. Transport of cosmic rays in chaotic magnetic fields. Phys. Rev. D 65, 023002 (2001).

    Article  ADS  Google Scholar 

  38. Fatuzzo, M., Melia, F., Todd, E. & Adams, F. C. High-energy cosmic-ray diffusion in molecular clouds: a numerical approach. Astrophys. J. 725, 515–527 (2010).

    Article  ADS  Google Scholar 

  39. Crutcher, R. M. Magnetic fields in molecular clouds: observations confront theory. Astrophys. J. 520, 706–713 (1999).

    Article  ADS  Google Scholar 

  40. Urquhart, J. S. et al. ATLASGAL—towards a complete sample of massive star forming clumps. Mon. Not. R. Astron. Soc. 443, 1555–1586 (2014).

    Article  ADS  Google Scholar 

  41. Albertsson, T., Kauffmann, J. & Menten, K. M. Atlas of cosmic-ray-induced astrochemistry. Astrophys. J. 868, 40 (2018).

    Article  ADS  Google Scholar 

  42. Ivlev, A. V. et al. Penetration of cosmic rays into dense molecular clouds: role of diffuse envelopes. Astrophys. J. 855, 23 (2018).

    Article  ADS  Google Scholar 

  43. Grenier, I. A., Casandjian, J.-M. & Terrier, R. Unveiling extensive clouds of dark gas in the solar neighborhood. Science 307, 1292–1295 (2005).

    Article  ADS  Google Scholar 

  44. Planck Collaboration et al. Planck early results. XIX. All-sky temperature and dust optical depth from Planck and IRAS. Constraints on the ‘dark gas’ in our Galaxy. Astron. Astrophys. 536, A19 (2011).

    Article  Google Scholar 

  45. Vladimirov, A. E. et al. GALPROP WebRun: an internet-based service for calculating galactic cosmic ray propagation and associated photon emissions. Comput. Phys. Commun. 182, 1156–1161 (2011).

    Article  ADS  MATH  Google Scholar 

  46. Ajello, M. et al. 3FHL: the third catalog of hard Fermi-LAT sources. Astrophys. J. Suppl. Ser. 232, 18 (2017).

    Article  ADS  Google Scholar 

  47. Lande, J. et al. Search for spatially extended Fermi Large Area Telescope sources using two years of data. Astrophys. J. 756, 5 (2012).

    Article  ADS  Google Scholar 

  48. Abdo, A. A. et al. Fermi LAT discovery of extended gamma-ray emission in the direction of supernova remnant W51C. Astrophys. J. Lett. 706, L1–L6 (2009).

    Article  ADS  Google Scholar 

  49. 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 

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

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

    Article  Google Scholar 

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

    Article  Google Scholar 

  53. Luhman, K. L., Esplin, T. L. & Loutrel, N. P. A census of young stars and brown dwarfs in IC 348 and NGC 1333. Astrophys. J. 827, 52 (2016).

    Article  ADS  Google Scholar 

  54. Zucker, C. et al. A large catalog of accurate distances to local molecular clouds: the Gaia DR2 edition. Astrophys. J. 879, 125 (2019).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

R.-z.Y. is supported by the NSFC under grants 12041305, 11421303 and the national youth thousand talents programme in China. G.-X.L. acknowledges support from NSFC grants 12273032, 1227030463, W820301904 and 12033005. B.L. acknowledges support from the NSFC under grant 12103049. Y.-D.C. is supported by the Ministry of Education of China and the China Manned Space Project (No. CMS-CSST- 2021-B09).

Author information

Author notes

  1. These authors contributed equally: Rui-zhi Yang, Guang-Xing Li, Bing Liu.

Authors and Affiliations

  1. Deep Space Exploration Laboratory/School of Physical Sciences, University of Science and Technology of China, Hefei, China

    Rui-zhi Yang & Bing Liu

  2. CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, China

    Rui-zhi Yang & Bing Liu

  3. School of Astronomy and Space Science, University of Science and Technology of China, Hefei, China

    Rui-zhi Yang & Bing Liu

  4. South-Western Institute for Astronomy Research (SWIFAR), Yunnan University (YNU), Kunming, P. R. China

    Guang-Xing Li

  5. Deutsches Elektronen Synchrotron DESY, Zeuthen, Germany

    Emma de Oña Wilhelmi

  6. School of Physics and Astronomy, Sun Yat-Sen University, Guangzhou, China

    Yu-Dong Cui

  7. Dublin Institute for Advanced Studies, Dublin, Ireland

    Felix Aharonian

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

    Felix Aharonian

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

    Felix Aharonian

Authors
  1. Rui-zhi Yang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Guang-Xing Li
    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

  4. Yu-Dong Cui
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Bing Liu
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Felix Aharonian
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

R.-z.Y., G.-X.L. and B.L. contributed to the paper in equivalent fractions. R.-z.Y., B.L. and E.d.O.W. performed the data analysis, G.-X.L., R.z.Y., Y.-D.C. and F.A. were responsible for the interpretation part and all authors contributed to the manuscript writing.

Corresponding author

Correspondence to Rui-zhi Yang.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

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

Additional information

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

Supplementary information

Supplementary Information

Supplementary Figs. 1–9 and Table 1.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Yang, Rz., Li, GX., Wilhelmi, E.d.O. et al. Effective shielding of ≲10 GeV cosmic rays from dense molecular clumps. Nat Astron 7, 351–358 (2023). https://doi.org/10.1038/s41550-022-01868-9

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41550-022-01868-9

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