Dark matter is the dominant form of matter in the Universe, but its nature is unknown. It is plausibly an elementary particle, perhaps the lightest supersymmetric partner of known particle species1. In this case, annihilation of dark matter in the halo of the Milky Way should produce γ-rays at a level that may soon be observable2,3. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps4,5 (perhaps smaller even than the Earth), which would be most easily detected where they cluster together in the dark matter haloes of dwarf satellite galaxies6. Here we report that such small-scale structure will, in fact, have a negligible impact on dark matter detectability. Rather, the dominant and probably most easily detectable signal will be produced by diffuse dark matter in the main halo of the Milky Way7,8. If the main halo is strongly detected, then small dark matter clumps should also be visible, but may well contain no stars, thereby confirming a key prediction of the cold dark matter model.
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We thank the Leibniz Supercomputing Centre of the Bavarian Academy of Sciences and Humanities, and the Computing Centre of the Max-Planck Society in Garching, where the simulations were carried out. C.S.F. acknowledges a Royal Society-Wolfson Research Merit award. This work was supported in part by an STFC Rolling Grant to the ICC.
This file contains Supplementary Notes, Supplementary Figures 5-8 and Supplementary References. The signal-to-noise calculation and the treatment of the background are described in detail and all-sky maps of the different emission components are shown. (PDF 453 kb)
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Springel, V., White, S., Frenk, C. et al. Prospects for detecting supersymmetric dark matter in the Galactic halo. Nature 456, 73–76 (2008). https://doi.org/10.1038/nature07411
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