High-frequency gravitational waves (HFGWs) in the MHz–GHz range can convert into radio photons in astrophysical magnetic fields via the inverse Gertsenshtein effect. It is shown that existing radio telescopes such as CHIME and FAST are excellent tools for detecting HFGW sources, significantly outperforming many dedicated experiments in the search for primordial black hole mergers—the most realistic sources of transient HFGWs. Radio telescopes also possess unique sensitivity to monochromatic HFGW radiation, for example, from clouds of ultralight bosons formed via superradiance around primordial black holes. These results point to a high probability of detecting HFGWs with currently operating radio observatories, opening a new observational window into astrophysics.
Gravitational waves are invisible vibrations of space itself, like the sound of a giant cosmic string. Ordinary detectors pick up the low 'notes' from the merger of large black holes. But there are also high-frequency gravitational waves — ultra-fast shudders, born from microscopic primordial black holes left over from the Big Bang. Flying through the Universe's magnetic fields, these vibrations turn into radio waves — like an acoustic guitar plugged into an amplifier suddenly sending out an electric signal. Radio telescopes like CHIME and FAST catch this signal, allowing us to hear the previously unheard. But most unexpectedly, clouds of invisible ultralight particles swarming around black holes can emit similar waves. If we catch their monochromatic 'ring,' it could be the key to unraveling dark matter — the mysterious substance that holds galaxies together.
🎯 The CHIME radio telescope, originally built to search for mysterious fast radio bursts, accidentally turned out to be an ideal gravitational wave detector.