X-ray Observations Uncover Hidden Disturbances in Abell 3571 Galaxy Cluster

Using the Einstein Probe (EP), astronomers from China and Germany have observed a nearby galaxy cluster known as Abell 3571. Results of the observational campaign, published January 8 on the arXiv pre-print server, provide more insights into the X-ray properties and structure of this cluster. Enormous structures 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. Abell 3571, or A3571, is a rich galaxy cluster in the Shapley Supercluster, at a redshift of 0.039. It has a radius of about 5.5 million light years and its mass is estimated to be 910 trillion solar masses. The brightest cluster galaxy (BCG) of Abell 3571 is MCG–05–33–002, which exhibits a pronounced north-south elongation. Evidence of past mergers? Previous X-ray observations of Abell 3571 have found that it is morphologically relaxed—has an overall spherically symmetric structure with a central cooling flow. However, multiwavelength studies of this cluster have revealed a more complex dynamical history, suggesting that it underwent a merger or disturbance events. Therefore, in order to verify this, a team of astronomers led by Xinyi Zheng of the Beijing Normal University in China has employed EP's Follow-up X-ray Telescope (FXT) to investigate Abell 3571. Their study was complemented by optical data from the DESI Legacy Imaging Surveys. Zheng's team found that Abell 3571 exhibits a relatively regular morphology. Both the surface brightness and temperature profiles showcase typical cool-core characteristics. However, although the X-ray morphology of this cluster looks relaxed, its residual map and 2D thermodynamic maps reveal disturbed structure in the inner region. Furthermore, the observations identified two prominent regions of surface brightness excesses within 20 arcminutes of the cluster center, located to the north and southwest. The southwestern excess appears to be associated with high-temperature features, while the northern excess corresponds to a cooler structure, which is most likely due to gas sloshing. Along the north-south direction When it comes to the temperature distribution of Abell 3571, the study found that it shows a pronounced north–south asymmetry. Moreover, a similar north–south elongation is seen in the optical galaxy density distribution. These findings suggest that the cluster's merger activity likely occurred along this axis. "We propose that the structure of A3571 originates from gas sloshing triggered by the off-axis passage of a low-mass subcluster moving from south to north. The sloshing displaces low-entropy gas from the cool core, producing a fan-shaped brightness excess to the north," the astronomers explain. Summing up the results, the authors of the paper conclude that despite its symmetric appearance, Abell 3571 is still recovering from a minor merger and is currently in a post-merger phase. © 2026 Science X Network