Skip to main content

Thank you for visiting 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.

A lower limit of Δz > 0.06 for the duration of the reionization epoch


Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies1. The observations are challenging, though, because of the low expected signal strength (10 mK), and contamination by strong (>100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature2,3,4 visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 < z < 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of Δz < 0.06 at the 95% confidence level.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Measured spectrum between 100 and 195 MHz.
Figure 2: Lower confidence bounds on the duration of the reionization transition. Statistical and systematic uncertainties are included.


  1. 1

    Furlanetto, S. R., Oh, S. P. & Briggs, F. H. Cosmology at low frequencies: the 21 cm transition and the high-redshift Universe. Phys. Rep. 433, 181–301 (2006)

    CAS  Google Scholar 

  2. 2

    Shaver, P. A., Windhorst, R. A., Madau, P. & de Bruyn, A. G. Can the reionization epoch be detected as a global signature in the cosmic background? Astron. Astrophys. 345, 380–390 (1999)

    CAS  Google Scholar 

  3. 3

    Gnedin, N. Y. & Shaver, P. A. Redshifted 21 centimeter emission from the pre-reionization era. I. Mean signal and linear fluctuations. Astrophys. J. 608, 611–621 (2004)

    CAS  Google Scholar 

  4. 4

    Furlanetto, S. R. The global 21-centimeter background from high redshifts. Mon. Not. R. Astron. Soc. 371, 867–878 (2006)

    CAS  Google Scholar 

  5. 5

    Zaldarriaga, M., Furlanetto, S. R. & Hernquist, L. 21 centimeter fluctuations from cosmic gas at high redshifts. Astrophys. J. 608, 622–635 (2004)

    CAS  Google Scholar 

  6. 6

    Madau, P., Meiksin, A. & Rees, M. J. 21 centimeter tomography of the intergalactic medium at high redshift. Astrophys. J. 475, 429–444 (1997)

    Google Scholar 

  7. 7

    Larson, D. et al. Seven-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: power spectra and WMAP-derived parameters. Preprint at 〈〉 (2010)

  8. 8

    Komatsu, E. et al. Seven-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: cosmological interpretation. Preprint at 〈〉 (2010)

  9. 9

    Bowman, J. D., Rogers, A. E. E. & Hewitt, J. N. Toward empirical constraints on the global redshifted 21 cm brightness temperature during the epoch of reionization. Astrophys. J. 676, 1–9 (2008)

    CAS  Google Scholar 

  10. 10

    Rogers, A. E. E. & Bowman, J. D. Spectral index of the diffuse radio background measured from 100 to 200 MHz. Astron. J. 136, 641–648 (2008)

    CAS  Google Scholar 

  11. 11

    Pritchard, J. R. & Loeb, A. Constraining the unexplored period between the dark ages and reionization with observations of the global 21 cm signal. Phys. Rev. D 82, 023006 (2010)

    Google Scholar 

  12. 12

    Pritchard, J. R., Loeb, A. & Wyithe, J. S. B. Constraining reionization using 21-cm observations in combination with CMB and Ly-α forest data. Mon. Not. R. Astron. Soc. 408 . 57–70 (2010)

  13. 13

    Pritchard, J. R. & Loeb, A. Evolution of the 21 cm signal throughout cosmic history. Phys. Rev. D 78, 103511 (2008)

    Google Scholar 

Download references


This work was supported by the NSF. J.D.B was supported during part of this work at the California Institute of Technology by NASA through a Hubble Fellowship awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy for NASA. This scientific work uses data obtained from the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. We thank CSIRO and Curtin University for logistical support and D. DeBoer, D. Herne, D. Emrich, M. Halleen and C. Halleen for on-site support.

Author information




Both authors contributed equally to the work in this paper.

Corresponding author

Correspondence to Judd D. Bowman.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Information comprising Description of the EDGES radio spectrometer, Analog-to-Digital Conversion, Compact, Planar, Dual-Octave Antenna and Ground Screen, Calibration and Data Interpretation, Selection of Observing Site, Supplementary Figures 1-2 with legends and additional references. (PDF 1108 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Bowman, J., Rogers, A. A lower limit of Δz > 0.06 for the duration of the reionization epoch. Nature 468, 796–798 (2010).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


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