1. Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85740 Garching, Germany
2. Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
3. Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia V8P 5C2, Canada
4. Department of Astronomy, University of Massachusetts, Amherst, Massachusetts 01003-9305, USA
5. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands

Correspondence to: V. Springel¹ Correspondence and requests for materials should be addressed to V.S. (Email: vspringel@mpa-garching.mpg.de).

Abstract

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 -rays at a level that may soon be observable^{2, 3}. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps^{4, 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 Way^{7, 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.

1. Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85740 Garching, Germany
2. Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
3. Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia V8P 5C2, Canada
4. Department of Astronomy, University of Massachusetts, Amherst, Massachusetts 01003-9305, USA
5. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands

Correspondence to: V. Springel¹ Correspondence and requests for materials should be addressed to V.S. (Email: vspringel@mpa-garching.mpg.de).

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