The century-old enigma of dark matter, this invisible substance thought to hold galaxies together, has just received a promising new clue thanks to modern technologies.
Scientists may be on the verge of confirming the existence of this elusive matter. Recent computer simulations indicate that a faint glow detected at the heart of the Milky Way could match the long-sought signature of dark matter. Moorits Muru, lead researcher of the study conducted at the Leibniz Institute for Astrophysics in Potsdam, believes this lead appears particularly credible although difficult to definitively prove.
Annotated artist's view of the Milky Way.
Image ESO.
Dark matter constitutes about 27% of the matter in the Universe but remains undetectable directly as it neither absorbs nor reflects light. The new simulations reveal that its distribution near the galactic center is not spherical as previously assumed, but flattened and ovoid. This shape strangely matches the gamma-ray pattern observed by NASA's Fermi space telescope, an abnormally intense signal detected since 2008 that extends across nearly 7000 light-years.
Two main hypotheses compete to explain this gamma emission: collisions of dark matter particles called WIMPs, or the activity of very rapidly rotating neutron stars called millisecond pulsars. Pulsars seemed favored because their distribution matched observations well, but new calculations show that dark matter can also adopt this particular configuration.
The team reconstructed the formation of the Milky Way using supercomputers, including the galactic collisions that marked its history. These violent events left their signature on the distribution of dark matter, giving it this flattened shape that now perfectly matches Fermi's data. Researchers emphasize that the two scenarios – dark matter and pulsars – have become almost impossible to distinguish with current instruments.
The next generation of observatories, like the Cherenkov Telescope Array Observatory (CTAO) which will enter service around the late 2020s, could settle the debate. Its superior resolution will allow differentiation between the energy signatures of pulsars and those of dark matter particles. Complementary observations of dwarf galaxies orbiting the Milky Way will also provide decisive elements for this major scientific quest.
WIMPs, leading candidates for dark matter
WIMPs (Weakly Interacting Massive Particles) represent one of the most serious hypotheses to explain the nature of dark matter. These hypothetical particles would interact very weakly with ordinary matter, which would explain why they remain undetectable despite their presumed abundance.
Their mass would be considerable compared to standard particles, perhaps hundreds of times greater than that of a proton. This property would make them particularly stable and difficult to produce in laboratories, but their mutual annihilation could generate detectable radiation such as the gamma rays observed at the galactic center.
Supersymmetric theories, extensions of the standard model of particle physics, naturally predict the existence of such particles. Their discovery would revolutionize our understanding of the Universe at both its smallest and largest scales.
Many underground experiments like XENONnT and LZ attempt to capture the rare recoil that a WIMP would produce when hitting an atomic nucleus, while gamma observatories like Fermi search for indirect signals of their annihilation.