 study has concluded that the velocities of the collision as currently measured are "incompatible with the prediction of a LCDM model".
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, resulting in a significant displacement between the clusters' center of visible matter and their gravitational potential.
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 dark matter to visible 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.
Mordehai Milgrom, the original proposer of MOND (Modified Newtonian Dynamics), has posted on-line a rebuttal of claims that the Bullet Cluster proves the existence of dark matter. Milgrom claims that MOND correctly accounts for the dynamics of galaxies outside of galaxy clusters, and even in clusters such as the Bullet Cluster it removes the need for most dark matter, leaving only a factor of two which Milgrom expects to be simply unseen ordinary matter (non-luminous baryonic matter) rather than cold dark matter. Without MOND, or some similar theory, the matter discrepancy in galaxy clusters is a factor of 10, i.e. MOND reduces this discrepancy five-fold to a factor of 2. Another study in 2006 cautions against "simple interpretations of the analysis of weak lensing in the bullet cluster", leaving it open that even in the non-symmetrical case of the Bullet Cluster, MOND, or rather its relativistic version TeVeS (Tensor–vector–scalar gravity), could account for the observed gravitational lensing.
- Abell 520 - a similar galaxy cluster whose dark and luminous matter have been separated during a major collision
- List of Galaxy Clusters
- Tucker, W.; Blanco, P.; Rappoport, S.; David, L.; Fabricant, D.; Falco, E. E.; Forman, W.; Dressler, A.; Ramella, M. (March 1998). "1E 0657-56: A Contender for the Hottest Known Cluster of Galaxies". Astrophysical Journal Letters (APJ) 496: L5. arXiv:astro-ph/9801120. Bibcode:1998ApJ...496L...5T. doi:10.1086/311234. Retrieved March 4, 2012.
- "NED results for object Bullet Cluster". NASA Extragalactic Database. Retrieved March 4, 2012.
- M. Markevitch; A. H. Gonzalez; D. Clowe; A. Vikhlinin; L. David; W. Forman; C. Jones; S. Murray & W. Tucker (2003). "Direct constraints on the dark matter self-interaction cross-section from the merging galaxy cluster 1E0657-56". Astrophys.J. 606 (2): 819–824. arXiv:astro-ph/0309303. Bibcode:2004ApJ...606..819M. doi:10.1086/383178.
- Harvard photo and description
- The dynamical status of the cluster of galaxies 1E0657-56
- M. Markevitch; S. Randall; D. Clowe; A. Gonzalez et al. (16–23 July 2006). "Dark Matter and the Bullet Cluster" (PDF). 36th COSPAR Scientific Assembly. Beijing, China. Abstract only
- Lunch-time talk at Harvard University by Scott Randall on 31 May 2006. Abstract only
- Clowe, Douglas et al. (2006). "A Direct Empirical Proof of the Existence of Dark Matter". The Astrophysical Journal Letters 648 (2): L109–L113. arXiv:astro-ph/0608407. Bibcode:2006ApJ...648L.109C. doi:10.1086/508162.
- Recent and Future Observations in the X-ray and Gamma-ray Bands
- Eric Hayashi; White (2006). "How Rare is the Bullet Cluster?". Mon.Not.Roy.Astron.Soc.Lett. 370: L38–L41. arXiv:astro-ph/0604443. Bibcode:2006MNRAS.370L..38H. doi:10.1111/j.1745-3933.2006.00184.x.
- Jounghun Lee; Komatsu (2010). "Bullet Cluster: A Challenge to LCDM Cosmology". ApJ 718. arXiv:1003.0939. Bibcode:2010ApJ...718...60L. doi:10.1088/0004-637X/718/1/60.
- A Clash of Clusters Provides New Clue to Dark Matter Newswise, Retrieved on September 1, 2008.
- G.W. Angus; B. Famaey & H. Zhao (September 2006). "Can MOND take a bullet? Analytical