XMM image of the southern XXL panorama. This is one half of the full XXL survey; along with the northern field XXL is the largest view of the deep X-ray sky obtained to date. The size of the full moon is shown for comparison. Most of the bright X-ray sources seen in this image are active galactic nuclei (more than 12,000 have been detected in this image). The red circles show the clusters of galaxies that were found in this image and that were used for the investigation of the evolution of galaxy clusters.
The XXL survey - S. Snowden, L. Faccioli, F. Pacaud
A panorama of the X-ray sky has been completed by an international team of more than 100 scientists, providing new insights into the nature of the Universe. The XXL team, which includes astrophysicists from the University of Bristol, used the European Space Agency's XMM-Newton X-ray observatory to take over 250 individual images of the sky. These were then stitched together to create two panoramas of remarkable sensitivity, one for the northern and one for the southern sky. The scientists used these deep XXL images to search for X-ray light from clusters of galaxies and from active galactic nuclei, supermassive black holes in the centres of galaxies. Such galaxy clusters are amazing laboratories in which to study the way that cosmic structures - from black holes to galaxies to the clusters themselves - have grown and evolved since the Big Bang. Moreover, their numbers and properties are sensitive to the conditions of the early universe and the details of its subsequent expansion. This means that, by carefully selecting, measuring and counting clusters of galaxies, scientists can infer hidden details of the nature of the Universe (such as the behaviour of the 'dark energy' that currently drives the expansion of the Universe).
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