Scientists report the first search for high‑frequency gravitational waves (HFGWs) in the gigahertz to terahertz band by looking for their conversion into radio light in Earth’s magnetic field. A gravitational wave passing through a magnetic field can, in theory, convert a tiny fraction of its energy into electromagnetic radiation. The team used sensitive archival data from the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) to look for that converted radio signal and found none above the noise level.

The conversion process the paper uses is called the inverse Gertsenshtein effect. In plain terms, it says a rippling of space (a gravitational wave) that crosses a magnetic field can produce a faint electromagnetic wave. The chance of conversion depends on the square of the magnetic field component perpendicular to the wave’s direction, integrated along the line of sight. Because Earth’s field extends across planetary scales, it offers a much larger “interaction volume” than small laboratory magnets, so the cumulative conversion can become measurable in principle. The authors used the International Geomagnetic Reference Field model (IGRF‑14) to map the field and compute where conversion is most likely on the sky.

For the search they combined wideband radio data that together cover roughly 1–1000 GHz. The paper states they analyzed 185 archival observations (listed as 17 from the VLA and 180 from ALMA) and processed them with standard radio analysis tools to remove interference and to mask known compact and extended radio sources. They assumed the hypothetical HFGW background was isotropic (the same in all directions) and unpolarized, and they averaged the predicted conversion probability over each telescope’s pointing path and observing time. They also note that radio propagation effects in the ionosphere can reduce conversion below about 10 GHz, but these plasma effects are negligible above 10 GHz.