Letter | Published:

The signature of the first stars in atomic hydrogen at redshift 20

Nature volume 487, pages 7073 (05 July 2012) | Download Citation


Dark and baryonic matter moved at different velocities in the early Universe, which strongly suppressed star formation in some regions1. This was estimated2 to imprint a large-scale fluctuation signal of about two millikelvin in the 21-centimetre spectral line of atomic hydrogen associated with stars at a redshift of 20, although this estimate ignored the critical contribution of gas heating due to X-rays3,4 and major enhancements of the suppression. A large velocity difference reduces the abundance of haloes1,5,6 and requires the first stars to form in haloes of about a million solar masses7,8, substantially greater than previously expected9,10. Here we report a simulation of the distribution of the first stars at redshift 20 (cosmic age of around 180 million years), incorporating all these ingredients within a 400-megaparsec box. We find that the 21-centimetre hydrogen signature of these stars is an enhanced (ten millikelvin) fluctuation signal on the hundred-megaparsec scale, characterized2 by a flat power spectrum with prominent baryon acoustic oscillations. The required sensitivity to see this signal is achievable with an integration time of a thousand hours with an instrument like the Murchison Wide-field Array11 or the Low Frequency Array12 but designed to operate in the range of 50–100 megahertz.

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This work was supported by the Israel Science Foundation (for R.B., and E.V.’s stay at Tel Aviv University) and by the European Research Council (for A.F.). D.T. and C.M.H. were supported by the US Department of Energy and the National Science Foundation. C.M.H. is also supported by the David & Lucile Packard Foundation.

Author information


  1. Jefferson Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

    • Eli Visbal
  2. Institute for Theory and Computation, Harvard University, 60 Garden Street, Cambridge, Massachusetts 02138, USA

    • Eli Visbal
  3. Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

    • Rennan Barkana
    •  & Anastasia Fialkov
  4. California Institute of Technology, Mail Code 350-17, Pasadena, California 91125, USA

    • Dmitriy Tseliakhovich
  5. California Institute of Technology, Mail Code 249-17, Pasadena, California 91125, USA

    • Christopher M. Hirata


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R.B. initiated the project, and E.V. made the computations and figures by developing a code, parts of which were based on codes supplied by A.F., D.T. and C.M.H. The text was written by R.B. and edited by the other authors. A.F. added the L–W module for Supplementary section 3 and made Supplementary Fig. 1.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Eli Visbal or Rennan Barkana.

Supplementary information

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  1. 1.

    Supplementary Information

    This file contains Supplementary Text and Data 1-4, which comprises 1) a description of the simulation code; 2) a comparison with previous work on the dark matter to baryon velocity difference; 3) the expected timing of the three high-redshift feedback transitions and 4) observational considerations. Supplementary Figure 1 (on the Lyman-Werner feedback) and additional references are also included.

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