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.
as written by the authors arXiv:2606.09968
High-frequency gravitational waves (HFGWs) in the MHz to GHz regime can convert into radio photons in the presence of astrophysical magnetic fields through the inverse Gertsenshtein effect. We show that existing radio telescopes like CHIME and FAST are excellent tools for detecting HFGW sources, significantly outperforming many existing experiments at detecting primordial black hole (PBH) mergers, the most realistic sources of transient HFGWs. Radio telescopes are also uniquely sensitive to sources of monochromatic HFGW emission, such as ultralight boson clouds formed through superradiance around PBHs, and are likely to have excellent sensitivity to generic sources of detectable HFGWs.
The CHIME radio telescope, originally built to search for mysterious fast radio bursts, accidentally turned out to be an ideal gravitational wave detector.