A mysterious electromagnetic signal detected around Earth may hold clues to the nature of dark matter, according to a new study published by Science Daily. The research, conducted by scientists from Kyoto University, Hiroshima University, and Nihon University, explored two leading hypotheses: ultralight axions and dark photons. In the mass range examined, these hypothetical particles would be roughly 19 to 21 orders of magnitude lighter than an electron.
Traditional experiments seek to detect axions by converting them into photons using powerful laboratory magnets, but these setups are limited by their small scale. To overcome this, the team proposed using Earth’s own magnetic environment as part of the detection system. “We asked ourselves whether we could use the Earth itself as a giant detector in the search,” said corresponding author Atsushi Taruya. The natural cavity formed between the Earth’s surface and the ionosphere acts as a resonator that amplifies electromagnetic waves in the targeted mass range.
Prior theoretical models were restricted to frequencies below 1 Hz, leaving a significant gap in potential search areas. The researchers developed a new framework incorporating atmospheric electrical conductivity, enabling reliable predictions up to approximately 30 Hz. Their calculations indicated that the Earth-ionosphere cavity could amplify signals near 8 Hz. The model also predicted distinct differences between the two candidates: axion signals should vary by location, peaking in Southeast Asia, while dark photon signals would appear with consistent strength globally.
To test these theories, the team analyzed a decade of geomagnetic data from the Eskdalemuir Observatory, operated by the British Geological Survey, spanning 2012 to 2022. After filtering out artificial noise, they searched for steady, narrow-band signals characteristic of long-term dark matter interactions. They applied the same methodology to dark photons, which can generate electromagnetic waves even without a magnetic field.
The results established new constraints on axion-light interactions that were about 100 times tighter than previous ground-based experiments and competitive with limits derived from astrophysical X-ray observations by observatories such as Chandra and NuSTAR. The search for dark photons yielded several intriguing signal candidates with potential dark matter origins, though their source remains unidentified and they have not been confirmed as evidence of dark matter.
While the true identity of dark matter remains unresolved, the study demonstrates that Earth’s natural electromagnetic environment can serve as a powerful tool for probing ultra-light dark matter forms and expanding future detection efforts.
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