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The signature of subgalactic dark matter clumping in the global 21-cm signal of hydrogen

Nature Astronomy volume 9, pages 1723–1731 (2025)Cite this article

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Abstract

It is thought that the Universe went through an early period known as the Dark Ages, during which primeval density fluctuations grew to form the first luminous objects, marking the beginning of cosmic dawn around 100 million years after the Big Bang. The 21-cm line of hydrogen atoms is the most promising probe of these epochs, with extensive observational efforts underway. Here we combine hydrodynamical simulations with a large-scale grid to precisely calculate the effect of nonlinear structure formation on the global (sky-averaged) 21-cm radio intensity. We show that it presents a potential opportunity to probe the properties of dark matter in a new regime, corresponding to a length-scale of only 150,000 light years and a mass scale of 20 million solar masses. This effect can in principle be detected unambiguously during the Dark Ages, where the weak signal requires an array of global signal antennae. During cosmic dawn, when stellar radiation boosts the signal, a single global antenna suffices, but the clumping effect must then be separated from the effect of the stars. Our findings open new avenues for testing the nature of dark matter as well as non-standard cosmological models.

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Fig. 1: Clumping effect in structure-formation simulations and resulting 21-cm signal.
Fig. 2: Predicted global 21-cm signal.

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Data availability

Intermediate data products such as snapshots of three-dimensional hydrodynamical simulations are available upon request to the corresponding author. Source data are provided with this paper.

Code availability

CAMB is available at http://camb.info. The BCCOMICS package is available via GitHub at https://github.com/KJ-Ahn/BCCOMICS. The GADGET code used for this work is available upon request to the corresponding author.

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Acknowledgements

H.P. thanks K. Moriwaki, Y. Hidenobu and K. Ahn for helpful comments on this work. H.P. also thanks J. Dhandha for providing his simulation data. H.P. was supported in part by grant NSF PHY-2309135 to the Kavli Institute for Theoretical Physics (KITP). Numerical simulations for this work were performed on the idark computing cluster of the Kavli Institute for Physics and Mathematics of the Universe, the University of Tokyo. R.B. and S.S. acknowledge the support of the Israel Science Foundation (grant nos. 2359/20 and 1078/24). R.M. is supported by the NITC FRG Seed Grant (grant no. NITC/PRJ/PHY/2024-25/FRG/12). N.Y. acknowledges financial support from JSPS International Leading Research 23K20035. R.B. and N.Y. acknowledge JSPS Invitational Fellowship S24099.

Author information

Authors and Affiliations

  1. Center for Computational Sciences, The University of Tsukuba, Tsukuba, Japan

    Hyunbae Park

  2. Computational Cosmology Center, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Hyunbae Park

  3. Kavli Institute for the Physics and Mathematics of the Universe, Kashiwa, Japan

    Hyunbae Park, Rennan Barkana & Naoki Yoshida

  4. School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel

    Rennan Barkana & Sudipta Sikder

  5. Department of Physics, The University of Tokyo, Bunkyo, Japan

    Naoki Yoshida

  6. Max-Planck-Institut für Astrophysik, Garching, Germany

    Naoki Yoshida

  7. Department of Physics, National Institute of Technology Calicut, Calicut, India

    Rajesh Mondal

  8. Institute of Astronomy, University of Cambridge, Cambridge, UK

    Anastasia Fialkov

  9. Kavli Institute for Cosmology, Cambridge, UK

    Anastasia Fialkov

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  1. Hyunbae Park
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  2. Rennan Barkana
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  4. Sudipta Sikder
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  6. Anastasia Fialkov
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Contributions

R.B. initiated the project. N.Y. and H.P. developed the numerical codes. H.P. ran the simulations, wrote the text and produced most of the figures in consultation with R.B. and N.Y. S.S. interpolated the simulation results, ran the large-scale grid and made Fig. 2, in consultation with R.B. and A.F., and using the 21CMSPACE code originally developed by A.F. and R.B. R.M. calculated the observational detection significance. All the authors edited the text.

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Correspondence to Hyunbae Park.

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Supplementary Figs. 1–11.

Supplementary Video 1 (download MOV )

SPH particles with spin temperature colour-coded in the CDM simulation.

Supplementary Video 2 (download MOV )

SPH particles with spin temperature colour-coded in the WDM simulation.

Supplementary Video 3 (download MOV )

SPH particles with gas temperature colour-coded in the CDM simulation.

Supplementary Video 4 (download MOV )

Gas temperature and spin temperature versus density relation in the CDM simulation.

Source data

Source Data Fig. 1 (download TXT )

ASCII file for the data points in the bottom panel.

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Park, H., Barkana, R., Yoshida, N. et al. The signature of subgalactic dark matter clumping in the global 21-cm signal of hydrogen. Nat Astron 9, 1723–1731 (2025). https://doi.org/10.1038/s41550-025-02637-0

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