Bullet Cluster

Galaxy cluster
name = Bullet Cluster


caption = X-ray photo by Chandra X-ray Observatory. Exposure time was 140 hours. The scale is shown in megaparsecs. Redshift ("z") = 0.3, meaning its light has wavelengths stretched by a factor of 1.3.
ra = 06h 58m 37.9s
dec = -55º 57' 0"
distance = 4 billion
constellation = Carina
main_member =
names = 1E 0657-56The Bullet cluster (1E 0657-56) consists of two colliding clusters of galaxies. [It is not an open cluster or "cluster of stars" which is "also" sometimes called a "Galactic cluster".] Studies of the Bullet cluster, announced in August 2006, provide the best evidence to date for the existence of dark matter. [ [http://arxiv.org/pdf/astro-ph/0309303 Direct constraints on the dark matter self-interaction cross-section from the merging galaxy cluster 1E 0657-56] ] The major components of the cluster pair, stars, gas and the putative dark matter, behave differently during collision, allowing them to be studied separately. The stars of the galaxies, observable in visible light, were not greatly affected by the collision, and most passed right through, gravitationally slowed but not otherwise altered. The hot gas of the two colliding components, seen in X-rays, represents most of the mass of the ordinary (baryonic) matter in the cluster pair. The gases interact electromagnetically, causing the gases of both clusters to slow much more than the stars. The third component, the dark matter, was detected indirectly by the gravitational lensing of 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.

The Bullet cluster is one of the hottest known clusters of galaxies. Observed from Earth, the subcluster passed through the cluster center 150 million years ago creating a "bow-shaped shock wave located near the right side of the cluster" formed as "70 million degree Celsius gas in the sub-cluster plowed through 100 million degree Celsius gas in the main cluster at a speed of about 6 million miles per hour". [ [http://chandra.harvard.edu/photo/2002/0066/ Harvard photo and description] ] [ [http://spaceimages.com/1e065756.html spaceimages.com] ] [ [http://edpsciences-usa.org/articles/aa/abs/2002/18/aah3368/aah3368.html The dynamical status of the cluster of galaxies 1E0657-56] ] Strictly speaking, the name "Bullet cluster" refers to the smaller subcluster, moving away from the larger one.

It provides the best current evidence for the nature of dark matter [ [http://cosis.net/abstracts/COSPAR2006/02655/COSPAR2006-A-02655.pdf Dark Matter and the Bullet Cluster by Markevitch] ] and provides "evidence against some of the more popular versions of Modified Newtonian Dynamics (MOND)." [ [http://hea-www.harvard.edu/LUNCH_TALKS/abstracts.html harvard.edu] ] "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." [ [http://google.com/search?q=cache:tOaYtMn8ep0J:arxiv.org/pdf/astro-ph/0512012+bullet-cluster+dark-matter Recent and Future Observations in the X-ray and Gamma-ray Bands] ]

" [T] he 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." [ [http://www.strw.leidenuniv.nl/~franx/astroph/2006apr28.html leidenuniv.nl] How Rare is 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 and provide an independent confirmation of what was detected in the Bullet cluster. [ [http://newswise.com/articles/view/543808/ A Clash of Clusters Provides New Clue to Dark Matter] Newswise, Retrieved on September 1, 2008.]

ources and notes

Further reading

* arXiv: [http://arxiv.org/abs/astro-ph/0608407 A direct empirical proof of the existence of dark matter]
* arXiv: [http://arxiv.org/abs/astro-ph/0608408 Strong and weak lensing united III: Measuring the mass distribution of the merging galaxy cluster 1E0657-56] (Marusa Bradac) Fri, 18 Aug 2006 20:06:48 GMT
* arXiv: [http://arxiv.org/abs/astro-ph/0606216 Can MOND take a bullet? Analytical comparisons of three versions of MOND beyond spherical symmetry]
* arXiv: [http://arxiv.org/abs/astro-ph/0609125 On the Law of Gravity, the Mass of Neutrinos, and the Proof of Dark Matter]
* arXiv: [http://arxiv.org/abs/astro-ph/0702146 The Bullet Cluster 1E0657-558 evidence shows Modified Gravity in the absence of Dark Matter] Brownstein and Moffat
* CXO: [http://chandra.harvard.edu/chronicle/0306/devil/ Bedeviling Devil's Advocate Cosmology] (The Chandra Chronicles) August 21, 2006
* CXO: [http://chandra.harvard.edu/photo/2006/1e0657/ 1E 0657-56: NASA Finds Direct Proof of Dark Matter]
* Harvard [http://chandra.harvard.edu/photo/2006/1e0657/media/bullet.mpg animation of the collision] showing how the dark matter and normal matter become separated.
* Harvard [http://cxc.harvard.edu/symposium_2005/proceedings/files/markevitch_maxim.pdf Harvard Symposium: Markevitch PDF] 36 color images and text pages proving the existence of Dark Matter from Bullet cluster data
* NASA: [http://nasa.gov/home/hqnews/2006/aug/HQ_06297_CHANDRA_Dark_Matter.html NASA Finds Direct Proof of Dark Matter] (NASA Press Release 06-297) Aug. 21, 2006
* Scientific American [http://sciam.com/article.cfm?chanID=sa003&articleID=000EB9FD-823F-14EB-823F83414B7F0000 Scientific American] article "SCIENCE NEWS August 22, 2006 Colliding Clusters Shed Light on Dark Matter" that includes a movie of a simulation of the collision