The Universe was nearly smooth and homogeneous before a redshift of z = 100, about 20 million years after the Big Bang1. After this epoch, the tiny fluctuations imprinted upon the matter distribution during the initial expansion began to collapse because of gravity. The properties of these fluctuations depend on the unknown nature of dark matter2,3,4, the determination of which is one of the biggest challenges in present-day science5,6,7. Here we report supercomputer simulations of the concordance cosmological model, which assumes neutralino dark matter (at present the preferred candidate), and find that the first objects to form are numerous Earth-mass dark-matter haloes about as large as the Solar System. They are stable against gravitational disruption, even within the central regions of the Milky Way. We expect over 1015 to survive within the Galactic halo, with one passing through the Solar System every few thousand years. The nearest structures should be among the brightest sources of γ-rays (from particle–particle annihilation).
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We thank A. Green, D. Schwarz, P. Jetzer, M. Miranda, A. Maccio and G. Bertone for discussions. All computations were performed on the zBox supercomputer at the University of Zurich. This work was supported by the Swiss National Science Foundation.
The authors declare that they have no competing financial interests.
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Diemand, J., Moore, B. & Stadel, J. Earth-mass dark-matter haloes as the first structures in the early Universe. Nature 433, 389–391 (2005). https://doi.org/10.1038/nature03270
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