Clusters are dynamic places - they are still in the process of being formed and so not all structure that is seen is a result of a radio source at the centre. Sometimes there are clusters of clusters on the sky, so-called Super-clusters, however these are very much still forming.
Clusters grow by merging with other clusters and groups of galaxies. Clusters formed from ripples in the matter density in the early universe. The gas and dark matter collapse down onto filaments, and clusters form at the junctions of these filaments. Material flows down the filaments onto the clusters and they are still forming. Some clusters show shock fronts as a smaller cluster ploughs into the cluster. In the case of 1E 0657-56 the shock waves are visible, like a bullet passing through gas.
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| 1E 0657-56; a merging cluster in which the bow shock formed by the supersonic motion of a sub-slump through the cluster is visible. (Image courtesy CHANDRA) |
In most cases these merger cannot be seen that clearly, but mapping the cluster's temperature can reveal shock fronts in the gas. The substructure shows that many clusters are still evolving.
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