Astronomers have traced the origins of an unusual radio structure resembling a musical treble clef to an ancient black hole outburst and the collision of two galaxy clusters, using NASA’s Chandra X-ray Observatory and other telescopes.
Nicknamed the “Treble Clef”, the formation was difficult to investigate because it lies almost directly behind the Milky Way’s disc, where stars, gas and dust obstruct observations. Researchers overcame this challenge by combining X-ray, radio and infrared data to study the region.
Observations from Chandra and Germany’s eROSITA X-ray telescope revealed vast quantities of superheated gas, confirming the presence of a galaxy cluster. Further analysis showed that two clusters are merging, with the collision likely occurring a few hundred million years ago.
According to the study, led by Andrea Botteon of Italy’s National Institute for Astrophysics and published in Astronomy & Astrophysics, the structure formed in two stages. An earlier outburst from a supermassive black hole propelled charged particles and magnetic fields into space at nearly the speed of light, generating radio emissions that gradually faded.
The subsequent cluster collision may have compressed or re-energised these ageing particle clouds, making them brighter in radio waves again. Shock waves produced by the collision could also have contributed to this process.
Radio observations from Europe’s LOFAR telescope revealed the distinctive shape, while X-ray analysis helped researchers identify evidence of the merger.
The resemblance to a treble clef is an example of pareidolia, the tendency to recognise familiar patterns in otherwise unrelated shapes. The structure has no known physical connection to musical notation.
