XMM-Newton Probes Formation Of Galaxy Clusters

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<b>XMM-Newton Probes Formation Of Galaxy Clusters</b><br /><br />LINK<br /><br />ESA’s X-ray observatory, XMM-Newton, has for the first time allowed scientists to study in detail the formation history of galaxy clusters, not only with single arbitrarily selected objects, but with a complete representative sample of clusters.<br /> <br />Knowing how these massive objects formed is a key to understanding the past and future of the Universe. <br />Scientists currently base their well-founded picture of cosmic evolution on a model of structure formation where small structures form first and these then make up larger astronomical objects. <br /><br />Galaxy clusters are the largest and most recently formed objects in the known Universe, and they have many properties that make them great astrophysical ‘laboratories’. For example, they are important witnesses of the structure formation process and important ‘probes’ to test cosmological models. <br /><br />To successfully test such cosmological models, we must have a good observational understanding of the dynamical structure of the individual galaxy clusters from representative cluster samples. <br /><br />For example, we need to know how many clusters are well evolved. We also need to know which clusters have experienced a recent substantial gravitational accretion of mass, and which clusters are in a stage of collision and merging. In addition, a precise cluster mass measurement, performed with the same XMM-Newton data, is also a necessary prerequisite for quantitative cosmological studies. <br /><br />The most easily visible part of galaxy clusters, i.e. the stars in all the galaxies, make up only a small fraction of the total of what makes up the cluster. Most of the observable matter of the cluster is composed of a hot gas (10-100 million degrees) trapped by the gravitational potential force of the cluster. This gas is completely invisible to human eyes,