Illustration of Abell 520 System (IMAGE)
Caption
An artist's illustration of the Abell 520 system shows where the bulk of the matter (blue) is found compared to the individual galaxies (yellow) and the hot gas (red) in the aftermath of a massive galaxy cluster collision. The material shown in blue is dominated by dark matter. As with the Bullet Cluster there are large separation between the regions where the galaxies are most common (peaks 2 and 4) and where most of the hot gas lies (peak 3). However, unlike the Bullet Cluster, a concentration of dark matter is found (peak 3) near the bulk of the hot gas, where very few galaxies are located. In addition, there is an area (peak 5) where there are several galaxies but very little dark matter. These observations conflict with the general understanding that dark matter and the galaxies should remain together, despite a violent collision. This raises questions about the current understanding of how dark matter behaves.
Credit
CXC/M. Weiss
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