Fundamental Research Division
The DRF at the CEA assemble approximately 6,000 scientists since January 2016.
Découvertes et avancées | Scientific result | Particle physics | Telescope | Black matter
The H.E.S.S. collaboration, which includes physicists from Irfu, has made ground-based observations in Namibia of gamma-ray sources detected by the Fermi space observatory that remain unidentified, otherwise known as Unidentified Fermi-LAT Objects (UFOs). These were suspected to be possible indicators of dark matters halos shining at very high energies, but the verdict now shows that UFOs are not actually these kinds of subhalos!
According to the standard model of cosmology, the dark matter particles of the primordial universe would have gradually formed "subhalos" under the effect of gravitation, which would have merged into increasingly massive "halos". Above a certain mass threshold, the halos would have begun to trap gas, which is behind the formation of stars and galaxies.
If the dark matter was composed of sufficiently massive WIMPs (Weakly Interacting Massive Particles), these particles could annihilate themselves through collisions within the subhalos, emitting very-high-energy gamma-rays (higher than 100 giga-electron volts) which would be detectable by the H.E.S.S. Cherenkov telescope network.
To test this hypothesis, the H.E.S.S. collaboration searched for unidentified gamma-ray sources – without any counterpart in the X-ray, visible or infrared domains – detected by the Large Area Telescope on NASA's Fermi satellite. They selected three of the most promising ones as potential dark matter subhalos (particles with energy around one teraelectron volt, e.g. 1012 eV or 1 TeV) and observed them.
While the subhalos composed of WIMPs were indeed thermally produced in the primordial universe, the researchers deduced from the H.E.S.S. observations that there are stronger constraints on the existence of WIMPs than those coming from Fermi. In the framework of cosmological models, these new constraints exclude the interpretation of the observed unidentified Fermi sources as galactic dark matter subhalos of energy in the TeV range.
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