Image of the Day: Dark Matter Clues of the ‘Bullet Cluster’


The Bullet cluster, one of the hottest known clusters of galaxies, provides the best current evidence for the nature of dark matter. Dark matter was detected indirectly by the gravitational lensing of the clusters background objects. In theories without dark matter, such as Modified Newtonian Dynamics, the lensing would be expected to follow the baryonic matter; i.e. the X-ray gas. However, the lensing is strongest in two separated regions near the visible galaxies. This provides support for the idea that most of the mass in the cluster pair is in the form of collisionless dark matter.

Compelling results were inferred from the Chandra observations of the 'bullet cluster',' which showed that the cluster is undergoing a high-velocity (around 4500 km/s) merger, evident from the spatial distribution of the hot, X-ray emitting gas, but this gas lags behind the subcluster galaxies. Furthermore, the dark matter clump, revealed by the weak-lensing map, is coincident with the collisionless galaxies, but lies ahead of the collisional gas.

The Daily Galaxy via Chandra Space Observatory

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