MEERKAT DISCOVERS UNUSUAL RADIO GLOW IN A DISTANT SWARM OF GALAXIES

A team of South African scientists using the South African Radio Observatory’s (SARAO) MeerKAT radio telescope has spotted a rare and extremely faint radio glow coming from a huge cluster of galaxies about 7 billion light-years away. This type of glow — called an ultra-steep- spectrum radio halo — is the most distant one ever found.

The discovery, led by Isaac Magolego, a PhD student at the University of the Witwatersrand (Wits), supervised by Professors Roger Deane and Kshitij Thorat, from Wits and the University of Pretoria, has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters. The student project is supported by the South African Radio Astronomy Observatory (SARAO).

Galaxy clusters are the largest objects in the universe held together by gravity, containing thousands of galaxies and enormous amounts of hot gas. The newly discovered radio glow sits at the centre of the cluster SPT-CLJ2337−5942, which has a mass of roughly a quadrillion times that of the Sun (a million billion).

Radio halos are produced when extremely energetic particles move through magnetic fields in galaxy clusters. This can happen when giant clusters crash into one another, stirring up powerful turbulence — similar to waves in a stormy sea — that re-energises older particles and makes them shine in radio light.

“At first, I thought this was a normal radio halo,” said Isaac Magolego. “But the detailed analysis revealed something far more unusual: the most distant ultra-steep-spectrum radio halo ever detected. It’s incredibly exciting, and I’m so grateful to SARAO for supporting my journey from undergraduate studies all the way to this discovery with MeerKAT in the final year of my PhD.” The shape of the radio glow also closely matches X-ray images of hot gas in the cluster, confirming the strong link between turbulence, magnetic fields, and energetic particles. Because the hotter Big Bang afterglow in the early universe makes it harder for such halos to shine, finding examples this far away is very important.

This result comes from the MeerKAT–South Pole Telescope (SPT) survey, a major international project combining MeerKAT’s world-leading radio sensitivity with high-frequency observations from the South Pole Telescope, a 10-metre diameter telescope at the Amundsen- Scott South Pole Station in Antarctica.

“This result highlights MeerKAT’s remarkable ability to reveal new important astrophysical laboratories in the distant universe – a key driver of our survey design strategy”, said Prof Roger Deane, co-lead of the MeerKAT-SPT survey with Prof Joaquin Vieira of the University of Illinois Urbana-Champaign.

Pontsho Maruping, Managing Director of SARAO, added: “This discovery highlights MeerKAT’s extraordinary sensitivity and the power of collaboration between SARAO, our universities, and global partners. It also reflects the impact of SARAO’s 20-year investment in human capital development, with Isaac’s achievement demonstrating the strength of our talent pipeline. As we enter the SKA era, MeerKAT continues to affirm South Africa’s leadership in cutting-edge radio astronomy.”

MeerKAT, operated by SARAO, continues to showcase South Africa’s growing leadership in global radio astronomy, and future observations with MeerKAT and the SKAO will help scientists understand how common these unusual radio halos are — and what they reveal about the early universe. So too does it continue to inspire young minds to explore the radio universe, with Isaac Magolego continuing his research as a SARAO postdoctoral fellow at the University of Pretoria in 2026.

The Letter reporting the findings has been accepted for publication will be available from the MNRAS Letters webpage in due course, but can be accessed from a pre-print server here.

Additional Information:

The South Pole Telescope (SPT) is a project led by the University of Chicago, with key partners including Argonne National Laboratory, Fermi National Accelerator Laboratory, the Harvard–Smithsonian Center for Astrophysics, UC Berkeley, McGill University, Case Western Reserve University, the University of Colorado Boulder, and other institutions across the SPT Collaboration. The telescope is supported primarily by the U.S. National Science Foundation through the United States Antarctic Program, with additional funding from the U.S. Department of Energy Office of Science, the Kavli Foundation, and the Gordon and Betty Moore Foundation.

Media Contact for Interviews:

Angus Flowers on aflowers@sarao.nrf.ac.za or on (076) 408 1593