Letter | Published:

Warm–hot baryons comprise 5–10 per cent of filaments in the cosmic web

Nature volume 528, pages 105107 (03 December 2015) | Download Citation

Abstract

Observations of the cosmic microwave background indicate that baryons account for 5 per cent of the Universe’s total energy content1. In the local Universe, the census of all observed baryons falls short of this estimate by a factor of two2,3. Cosmological simulations indicate that the missing baryons have not condensed into virialized haloes, but reside throughout the filaments of the cosmic web (where matter density is larger than average) as a low-density plasma at temperatures of 105−107 kelvin, known as the warm–hot intergalactic medium3,4,5,6. There have been previous claims of the detection of warm–hot baryons along the line of sight to distant blazars7,8,9,10 and of hot gas between interacting clusters11,12,13,14. These observations were, however, unable to trace the large-scale filamentary structure, or to estimate the total amount of warm–hot baryons in a representative volume of the Universe. Here we report X-ray observations of filamentary structures of gas at 107 kelvin associated with the galaxy cluster Abell 2744. Previous observations of this cluster15 were unable to resolve and remove coincidental X-ray point sources. After subtracting these, we find hot gas structures that are coherent over scales of 8 megaparsecs. The filaments coincide with over-densities of galaxies and dark matter, with 5–10 per cent of their mass in baryonic gas. This gas has been heated up by the cluster’s gravitational pull and is now feeding its core. Our findings strengthen evidence for a picture of the Universe in which a large fraction of the missing baryons reside in the filaments of the cosmic web.

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Acknowledgements

Work reported here is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. D.E. thanks F. Vazza, S. Paltani and S. Molendi for discussions. We thank H. Ebeling, M. Limousin, B. Clément, H. Atek, D. Harvey, E. Egami, M. Rexroth and P. Natarajan for help with writing the XMM-Newton proposal. M.J., H.I. and R.M. acknowledge support from the UK Science and Technology Facilities Council (grant numbers ST/L00075X/1, ST/H005234/1), the Leverhulme trust (grant number PLP-2011-003) and the Royal Society. J.-P.K. acknowledges support from the ERC advanced grant LIDA and from CNRS. H.Y.S. acknowledges support by a Marie Curie International Incoming Fellowship within the 7th European Community Framework Programme, and NSFC of China under grant 11103011. T.E. was supported by the Deutsche Forschungsgemeinschaft through the Transregional Collaborative Research Centre TR 33 ‘The Dark Universe’. E.J. was supported by CNES. J.R. acknowledges support from the ERC starting grant CALENDS.

Author information

Affiliations

  1. Department of Astronomy, University of Geneva, Chemin d’Ecogia 16, 1290 Versoix, Switzerland

    • Dominique Eckert
    •  & Céline Tchernin
  2. INAF – IASF Milano, Via E. Bassini 15, 20133 Milan, Italy

    • Dominique Eckert
  3. Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK

    • Mathilde Jauzac
    • , Holger Israel
    •  & Richard Massey
  4. Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Durban 4041, South Africa

    • Mathilde Jauzac
  5. Laboratoire d’Astrophysique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix, Switzerland

    • HuanYuan Shan
    •  & Jean-Paul Kneib
  6. Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France

    • Jean-Paul Kneib
    •  & Eric Jullo
  7. Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn, Germany

    • Thomas Erben
    •  & Matthias Klein
  8. CRAL, Observatoire de Lyon, Université Lyon 1, 9 Avenue Ch. André, F-69561 Saint Genis Laval Cedex, France

    • Johan Richard

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Contributions

D.E.: lead author, X-ray analysis. M.J.: weak and strong lensing analysis. H.Y.S.: CFHT weak lensing analysis. J.-P.K.: principal investigator of the XMM-Newton observation, strong and weak lensing analysis and identification of the red cluster sequence in the photometric data. T.E.: WFI and CFHT data reduction. H.I.: WFI and CFHT data reduction. E.J.: weak and strong lensing modelling techniques. M.K.: WFI and CFHT data reduction. R.M.: weak lensing analysis. J.R.: strong lensing analysis. C.T.: X-ray analysis.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Dominique Eckert.

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https://doi.org/10.1038/nature16058

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