Astronomers have employed the upgraded Giant Metrewave Radio Telescope (uGMRT) and the MeerKAT radio telescope to observe a galaxy cluster known as RXCJ0232–4420. Results of the new observations, published April 29 on the arXiv pre-print server, deliver important insights into the nature of this cluster.

Galaxy clusters contain up to thousands of galaxies bound together by gravity. They generally form as a result of mergers and grow by accreting sub-clusters. Therefore, they could serve as excellent laboratories for studying galaxy evolution and cosmology.

Galaxy cluster with a unique radio halo

RXCJ0232–4420 is a massive galaxy cluster at a redshift of approximately 0.066, discovered in 2002. It is a relaxed cool-core cluster hosting two brightest cluster galaxies (designated BCG-A and BCG-B), separated by about 330,000 light years.

Previous observations of RXCJ0232–4420 revealed diffuse emission centered on BCG-A, resembling a typical radio mini-halo, while some other studies found cluster-scale diffuse emission extending up to about 3.6 million light years, which is consistent with the size of a giant radio halo. Moreover, two candidate relics located east and south of the diffuse emission have also been identified.

Therefore, given that the radio halo of RXCJ0232–4420 is assumed to be much larger and more powerful than a typical mini-halo, rather than approaching the scale of a giant halo, the cluster is perceived as a unique system to probe how small radio structures might grow into giant ones. That is why a team of astronomers led by Pralay Biswas of the National Center for Radio Astrophysics in Pune, India, decided to take a closer look at RXCJ0232–4420 with uGMRT and MeerKAT.

As seen by uGMRT and MeerKAT

The observations found that the central radio emission in RXCJ0232–4420 extends beyond 3.3 million light years at all frequencies, which confirms the presence of a giant radio halo in this cluster. Moreover, an east radio relic was identified with a linear size of approximately 980,000 light years.

According to the paper, the radio halo and the candidate east relic have spectral indices of -1.17 and -0.85, respectively. The e-folding radius of the halo's radio profile shows no significant frequency variation, which indicates that there is no radial spectral steepening over different frequencies.

The spectral index maps of RXCJ0232–4420 exhibit minimal variation in spectral indices across pixels. It turned out that most of the pixels have spectral indices of around −1.0 to −1.3, which are not very steep for a radio halo with a cool core. This finding suggests that in-situ re-acceleration of charged particles is occurring at small scales throughout the cluster region.

The study also found that point-to-point radio and X-ray surface brightness correlation analysis shows a strong positive correlation between the non-thermal and thermal parts of the intracluster medium of RXCJ0232–4420.

Furthermore, the X-ray morphology and thermodynamic properties indicate that it is an intermediate dynamical system, hosting a cool core while showing evidence for mild substructure.

Written for you by our author Tomasz Nowakowski, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

© 2026 Science X Network