Scientists from Japanese universities have developed a novel approach to detecting dark matter by leveraging Earth’s natural electromagnetic environment. Dark matter comprises roughly a quarter of the universe’s total energy content, yet its composition remains unknown. Among leading theoretical candidates are ultralight axions and dark photons, particles that would be extraordinarily small—roughly 19 to 21 orders of magnitude lighter than electrons.
Traditional laboratory experiments attempting to detect axions rely on converting them to photons using powerful magnetic fields, but this method is limited by the small area these magnets can cover. Researchers from Kyoto University, Hiroshima University, and Nihon University proposed using Earth itself as a detector. The region between Earth’s surface and the ionosphere naturally resonates with electromagnetic waves, functioning similarly to a large cavity that amplifies signals in specific frequency ranges relevant to ultralight dark matter particles.
Previous theoretical models could only reliably describe frequencies below 1 Hz, leaving much of the potentially useful range unexplored. The research team developed an expanded theoretical framework incorporating atmospheric electrical conductivity, enabling reliable predictions up to approximately 30 Hz. This model also predicted distinguishing characteristics between the two dark matter candidates: axion signals should vary by geographic location with the strongest signals expected in Southeast Asia, while dark photon signals should appear relatively uniform globally.
The researchers analyzed approximately ten years of geomagnetic data collected from 2012 to 2022 by the British Geological Survey’s Eskdalemuir Observatory. After removing artificial noise sources, they searched for steady signals concentrated in narrow frequency ranges. The analysis produced notably stronger constraints on axion interactions—approximately 100 times tighter than previous ground-based experimental results and competitive with constraints from astrophysical observations.
The dark photon analysis identified several intriguing signal candidates with potential dark matter origins, though their sources remain unconfirmed. While dark matter’s identity continues to elude researchers, the new theoretical framework offers a promising pathway for future investigations using Earth’s natural electromagnetic properties to probe ultralight dark matter candidates.
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