A mysterious signal around Earth could be dark matter

Dark matter remains one of the greatest enigmas in modern physics, despite astronomers' high confidence in its existence. It is believed to make up around a quarter of the universe's total energy content, but scientists have yet to determine its composition. Two prominent hypotheses are ultralight axions and dark photons, both of which would be incredibly light, approximately 19 to 21 orders of magnitude lighter than an electron.

Traditional axion experiments attempt to convert axions into photons by subjecting them to extremely strong magnetic fields in laboratory settings. However, these experiments face a major limitation: even powerful laboratory magnets can only cover a limited area. Researchers from Kyoto University, Hiroshima University, and Nihon University have found a solution by utilizing Earth's magnetic environment as part of the experiment.

The Earth-ionosphere cavity, which acts as a natural resonator amplifying electromagnetic waves, is particularly useful for detecting signals associated with ultralight particles. The cavity's resonance with electromagnetic waves makes it especially suitable for searching for signals from the ultralight particles the researchers sought to investigate.

Initially, previous theory only covered frequencies below 1 Hz, leaving a broad range of potentially useful frequencies unexplored. To address this issue, the researchers developed a new theoretical framework that incorporates the electrical conductivity of the atmosphere, enabling them to predict signals up to about 30 Hz with greater accuracy.

The team analyzed approximately ten years of geomagnetic measurements collected between 2012 and 2022 by the British Geological Survey's Eskdalemuir Observatory. They first removed artificial sources of noise from the data, then searched for a steady signal within a very narrow frequency range that dark matter is expected to produce over extended periods.

Their findings were subjected to statistical analysis. The same theoretical approach was applied to dark photons, which can produce electromagnetic waves even without a magnetic field. Researchers identified several signal candidates that could potentially be of dark matter origin, although the source of these signals remains unknown and has not been confirmed as evidence of dark matter. Consequently, the true nature of dark matter remains unresolved.

Despite this, the novel theoretical framework offers researchers a powerful method to expand future searches and use Earth's natural electromagnetic environment as a tool for probing the lightest possible forms of dark matter.