Bold claim: South African scientists have identified the most distant ultra-steep-spectrum radio halo ever observed.
In a landmark finding, researchers from South Africa detected an exceptionally faint radio glow emanating from a colossal galaxy cluster roughly 7 billion light-years away. The discovery was announced by the South African Radio Astronomy Observatory (SARAO), which credited a MeerKAT telescope observation as the key to spotting this rare signal. This ultra-steep-spectrum radio halo represents the farthest example of its kind discovered to date.
Leading the investigation was Isaac Magolego, a PhD candidate at the University of the Witwatersrand (Wits), working with supervisors Professors Roger Deane and Kshitij Thorat from Wits and the University of Pretoria. The team’s findings have been submitted for publication in Monthly Notices of the Royal Astronomical Society: Letters.
The newly found glow sits at the core of the galaxy cluster SPT-CLJ2337-5942, a system with a mass about a quadrillion times that of the Sun. Radio halos like this arise when highly energetic particles interact with magnetic fields inside galaxy clusters, a process often driven by turbulence produced when enormous clusters collide.
“I initially assumed this was a typical radio halo,” Magolego explained in the SARAO release. “Yet detailed analysis revealed something much more extraordinary: the most distant ultra-steep-spectrum radio halo ever detected. It’s incredibly exciting.”
Magolego noted that the radio glow’s morphology aligns closely with X-ray images of hot cluster gas, reinforcing the connection between turbulence, magnetic fields, and energetic particles. Detecting such halos at this distance offers valuable clues about the conditions of the early universe, where the hotter Big Bang afterglow makes halo emission less common.
This discovery arose from the MeerKAT-South Pole Telescope survey, a major international collaboration that leverages MeerKAT’s leading radio sensitivity alongside high-frequency observations from the South Pole Telescope (SPT). The SPT is a 10-meter telescope housed at the Amundsen-Scott South Pole Station in Antarctica.
MeerKAT, an SARAO project situated in South Africa’s Karoo region, comprises 64 radio dishes and serves as a precursor to the Square Kilometre Array (SKA), slated to become the world’s largest telescope when science operations begin around 2028.
The South Pole Telescope (SPT) is directed by the University of Chicago with partners across the international SPT Collaboration, focusing on high-frequency observations of the distant cosmos.
