The Universe is not silent, and apart from what we observe with our eyes, much of what it says arrives as faint radio whispers that we are able to listen to if we tune into the right frequency. South Africa’s MeerKAT telescope has become one of the world’s finest listeners, revealing structures in deep space that were simply invisible to previous instruments. At the centre of this effort is the MeerKAT Galaxy Clusters Legacy Survey (MGCLS), a programme led by the South African Radio Astronomy Observatory (SARAO).
These clusters contain hundreds or thousands of galaxies, all immersed in a vast atmosphere of hot electrified gas. When clusters collide or merge, they leave behind an imprint of faint diffuse radio structures - large, faint clouds of emission produced by extremely fast-moving charged particles interacting with magnetic fields. These features act as tracers of cosmic upheaval. They show where shock waves have passed, where turbulence is stirred, and how magnetic fields thread through systems millions of light years wide.
The new MGCLS II catalogue, published at Monthly Notices of the Royal Astronomical Society, led by Rhodes University and SARAO researcher Dr Konstantinos Kolokythas, marks a significant advance. Following up on the MGCLS overview paper), it charts in detail the diffuse radio emission in 115 galaxy clusters, detecting these faint radio structures in more than half of them and expanding the known population to 103 structures; 60 of which had never been seen before.
This catalogue demonstrates what occurs when South African engineering is combined with South African scientific leadership,” Dr Kolokythas states. “MeerKAT has uncovered structures that were previously beyond the reach of earlier telescopes, and each one teaches us something more about how galaxy clusters grow, collide, and evolve.”
This work's value goes well beyond astrophysics. It highlights a research environment in South Africa that contributes directly to global knowledge, strengthens the country’s scientific standing, and trains researchers who will lead future projects with the Square Kilometre Array (SKA). It also demonstrates the tangible public benefit of long-term, curiosity-driven research: understanding the forces that shape galaxy clusters helps improve models of cosmic magnetism, large-scale structures, and the interaction between matter and magnetic fields under extreme conditions.
Diffuse radio emission is notoriously difficult to study. It is faint, spread out, and easily confused with unrelated signals from individual galaxies. MeerKAT’s sensitivity and image quality finally allow these structures to be separated, measured and understood with confidence. MGCLS II provides detailed information on their sizes, shapes, brightness and locations, backed by a comprehensive review of what is known about each cluster from decades of X-ray, radio and optical studies.
“We wanted to build something that will help the international community and that can be easily used,” Dr Kolokythas explains. “Every source in the catalogue has measured properties and high-quality images. It is a foundation for future work, not just a list of detections.”
The survey also emphasises the importance of studying clusters across different wavelengths. X-ray images reveal where hot gas is located in the cluster’s core, while optical data show the distribution of galaxies. When these are combined with MeerKAT’s radio observations, a clearer picture emerges. Halos in the centre tend to coincide with the densest X-ray gas, signalling turbulence caused by major mergers. Relics on the outskirts often align with sharp edges in X-ray brightness, providing evidence of shock waves sweeping through the cluster.
This kind of multi-wavelength research is vital for the future of global astronomy. As the SKA era approaches, MeerKAT is already setting the standards that future surveys will follow. The MGCLS work demonstrates what becomes achievable when instruments are designed not only to detect discrete objects but also to reveal the finest details of diffuse, low-surface-brightness structures that carry the history of cosmic events.
“MGCLS provides a glimpse of the discoveries that will become routine with the SKA,” Dr Kolokythas says. “If MeerKAT can uncover this much at 1.28 GHz, the full SKA will completely transform our understanding of how the largest structures in the universe form.”
The project also highlights Rhodes University’s strong research culture. Its radio astronomers lead international collaborations, shape the scientific agenda in cluster studies, and play a key role in actively contributing to the training pipeline that will supply expertise for the SKA. Their work positions the institution as a contributor to global science while also advancing South Africa’s strategic investment in radio astronomy.
For Dr Kolokythas, the appeal is both scientific and human. “What excites me most is that radio waves, which we cannot see or feel, allow us to trace the life cycle of galaxy clusters,” he says. “In those faint signals, the universe records the story of collisions, shocks and magnetic fields on unimaginable scales.”
MGCLS II is more than just a dataset; it is a benchmark. It offers the world an atlas of structures shaped by ancient cosmic events, enabled by South African infrastructure and scientific leadership. It demonstrates that cutting-edge research can stem from places dedicated to serving the common good, and that Rhodes University’s work – quiet, rigorous, and globally recognised – adds valuable insight into how humanity understands the Universe.
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