Image Courtesy: NASA
Physicists searching for dark matter have turned Earth into an enormous natural detector, analyzing a decade of magnetic-field data for signs of hypothetical particles that could explain some of the Universe’s biggest mysteries.
The experiment produced dozens of potential signals consistent with predicted properties of axions and dark photons, two proposed candidates for dark matter. The findings are far from proof, however, and the researchers acknowledge that the signals could have other explanations.
Dark matter is believed to account for much of the matter in the Universe, based on gravitational effects that cannot be explained by visible matter alone. Yet despite decades of research, scientists have not directly identified the substance or determined exactly what it is made of.
One leading possibility is the axion, a hypothetical particle first proposed in the 1970s. Unlike many dark matter candidates, axions are predicted to interact with electromagnetic fields. In strong magnetic fields, they could potentially convert into photons, producing a detectable electromagnetic signal.
Researchers led by Japanese theoretical physicist Atsushi Taruya proposed using Earth’s own environment to search for those signals. The Earth and ionosphere form a natural electromagnetic cavity that can resonate at frequencies corresponding to certain axion masses.
The team analyzed magnetic-field measurements collected by the British Geological Survey between 2012 and 2022. After accounting for background noise, the researchers identified 65 potential axion signals. Applying stricter statistical criteria reduced the number to 25.
The same data was also examined for dark photons, another hypothetical dark matter candidate that could behave differently from ordinary photons and potentially interact with electromagnetic fields. That analysis produced as many as 342 candidates under relaxed criteria, falling to 31 after applying stricter signal-to-noise requirements.
The biggest challenge is determining what, if anything, produced these signals. The current experiment cannot distinguish axions from dark photons, nor can it establish that either particle is responsible.
Future measurements could provide a crucial test. Axion-generated signals should vary with Earth’s magnetic field, while dark photon signals would not necessarily depend on it. Because Earth’s magnetic field changes across the planet, observations from multiple locations could reveal whether the signals have the expected geographic pattern.
The current dataset comes from a single observatory in the United Kingdom, making that comparison impossible for now. The researchers say measurements from additional experiments could provide the independent evidence needed to determine whether these strange signals are genuine clues to dark matter.
