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.


Hydrogen was not ionized abruptly


When and how the first stars and galaxies ionized the primordial hydrogen atoms that filled the early Universe is not known. Observations with a single radio antenna are opening a new window on the process. See Letter p.796

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: The 21-centimetre cosmic hydrogen signal.


  1. 1

    Loeb, A. How Did the First Stars and Galaxies Form? (Princeton Univ. Press, 2010).

    Book  Google Scholar 

  2. 2

    Bowman, J. D. & Rogers, A. E. E. Nature 468, 796–798 (2010).

    ADS  CAS  Article  Google Scholar 

  3. 3

    Furlanetto, S. R., Oh, S. P. & Briggs, F. H. Phys. Rep. 433, 181–301 (2006).

    ADS  CAS  Article  Google Scholar 

  4. 4

    Shaver, P. A., Windhorst, R. A., Madau, P. & de Bruyn, A. G. Astron. Astrophys. 345, 380–390 (1999).

    ADS  CAS  Google Scholar 

  5. 5

    Becker, R. H. et al. Astron. J. 122, 2850–2857 (2001).

    ADS  Article  Google Scholar 

  6. 6

    Komatsu, E. et al. Astrophys. J. Suppl. Ser. 180, 330–376 (2009).

    ADS  Article  Google Scholar 

  7. 7

    Robertson, B. E., Ellis, R. S., Dunlop, J. S., McLure, R. J. & Stark, D. P. Nature 468, 49–55 (2010).

    ADS  CAS  Article  Google Scholar 

  8. 8

    Pritchard, J. R. & Loeb, A. Phys. Rev. D 82, 023006 (2010).

    ADS  Article  Google Scholar 

  9. 9

    Santos, M. G. et al. Astrophys. J. 689, 1–16 (2008).

    ADS  CAS  Article  Google Scholar 

Download references

Author information



Rights and permissions

Reprints and Permissions

About this article

Cite this article

Pritchard, J., Loeb, A. Hydrogen was not ionized abruptly. Nature 468, 772–773 (2010).

Download citation


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