|
|
XMM-Newton probes formation of galaxy clusters   This X-ray image shows the cluster RXCJ0658.5-5556, a violently merging cluster. The dark blue region near the centre is the core of a sub-cluster flying through the main cluster body at high ‘supersonic’ speed, as indicated by a mach cone in front of this region. This sub-cluster had a pronounced low entropy core region that so far survived and is still visible.
In front of the bow shock region (to the right of the blue region) we see a very dramatic entropy enhancement marked by an arrow which is the cluster gas heated by the shock front caused by the fast flying sub-cluster ‘bullet’. This is the first direct X-ray evidence of shock heating in merging clusters.  This X-ray image of cluster RXCJ2337.6+0016, shows a cluster merger configuration in a very late stage. The two merging sub-clusters are dissolved in the new cluster but we still see a very complex entropy structure in the centre.
The blue irregular-shaped region in the centre has the low entropy of a cool cluster core. It was probably a stable, very symmetrical, cool and dense cluster core region that has now completely been disrupted by the cluster merger.  This X-ray image of galaxy cluster RXCJ 0232.2-4420, shows a less violent case. This cluster has a more regular appearance, except for the low entropy zone in the top left sector (arrow). Such a low entropy structure is expected and also seen in simulations when warm gas (colder than the cluster gas) flows into the cluster from a large-scale structure filament. Release date: 31 August 2005 |