Significance To Dark Matter
The Bullet Cluster provides the best current evidence for the nature of dark matter and provides "evidence against some of the more popular versions of Modified Newtonian Dynamics (MOND)" as applied to large galactic clusters.
"Particularly compelling results were inferred from the Chandra observations of the 'bullet cluster' (1E0657-56; Fig. 2) by Markevitch et al. (2004) and Clowe et al. (2004). Those authors report 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. This—and other similar observations—allow good limits on the cross-section of the self-interaction of dark matter."
"The velocity of the bullet subcluster is not exceptionally high for a cluster substructure, and can be accommodated within the currently favoured Lambda-CDM model cosmogony."
In an independent confirmation of results from the Bullet Cluster, more recent observations of the cluster MACS J0025.4-1222 indicate that a titanic collision has separated the dark from ordinary matter.
However, while the Bullet Cluster phenomenon may provide direct evidence for dark matter on large cluster scales, it offers no specific insight into the original galaxy rotation problem. In fact, the observed ratio of visible matter to dark matter in a typical rich galaxy cluster is much lower than predicted. This may indicate that the prevailing cosmological model is insufficient to describe the mass discrepancy on galaxy scales, or that its predictions about the shape of the universe are incorrect.
Read more about this topic: Bullet Cluster
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