Talk:Bullet Cluster

message: The Problems section does not cite sources, and is misleading if not plainly inaccurate.  
It begins by stating that the bullet cluster provides no insight into the galactic rotation problem.  However, the bullet cluster does provide support for the existence of dark matter, as described and cited in the "Overview" section.  Dark matter _is_ the most widely accepted explanation of the galactic rotation problem (see the wikipedia page on Galaxy Rotation Curve).
The next sentences are "Dark matter has not yet been observed on galactic scales, where (if dark matter exists) the high frequency of collisions should produce phenomena similar to the Bullet Cluster. No such phenomena have been observed."
However, dark matter has been observed, indirectly, through gravitational lensing effects, and has _only_ been observed in this manner on galactic scales.  The author also suggests that collisions like the bullet cluster should be common.  While it is true that galactic mergers are not uncommon, the 2006 paper by Hayashi, et. al. concludes that the liklihood of a galactic collision occuring with speeds like those of the bullet cluster's subcluster are 1 in 500, "a rare but not impossible event in the currently favored Lambda-CDM cosmology".(http://arxiv.org/abs/astro-ph/0604443v1 "How Rare Is the Bullet Cluster?")
I am confused by the idea that "no such phenomena have been observed" on a page about such an observed phenomenon.
And while critics of Dark Matter, such as Milgrom, the creator of the Modified Newtonian Dynamics theory, cited by the author of this section, would believe that there is enough cold nonluminous particulate baryonic matter in the universe to explain the bullet cluster, it is a false assertion that astronomers in general expect there to be enough cold, non-diffuse baryonic matter to explain the discrepancy in the mass centroid locations with the location of the stripped gases of the bullet cluster.  Most astronomers accept dark matter as the explanation for missing mass in the universe.  Even MOND proponents do not suggest that a purely baryonic MOND explains the bullet cluster, as in the link provided by the author of the problems section.
-- Venus19000 (talk) 04:16, 21 November 2009 (UTC)
thread_title:  Dubious "Problems" section 

message: The two articles Bullet cluster and Bullet cluster of galaxies were created within a few hours of each other, and should be merged.  The article at Bullet cluster is better developed, so we can basically keep that one.  As far as the name, I chose Bullet cluster of galaxies to match the articles at Virgo cluster of galaxies and Coma cluster of galaxies, so I suggest the article be placed at Bullet cluster of galaxies. --Reuben 18:42, 16 August 2006 (UTC)
replies: text: I merged them here. Everyone please feel free to improve the article but I suggest waiting until NASA's announcement on Monday before dealing with the scientific details (the exact specs - the numbers) of what we know about dark matter due to the bullet cluster. I also suggest waiting until then to decide on the best title for the article. One thing I don't know right now is whether "Bullet Cluster" or "Bullet cluster" is better. WAS 4.250 23:37, 16 August 2006 (UTC)
replies: text: There's actually quite a lot known about the Bullet cluster now.  I expect the upcoming Chandra result will be an incremental improvement on the X-ray gas component; it shouldn't change anything about the DM density and location, inferred from weak lensing.  I suggest the style "Bullet cluster of galaxies" for consistency with other cluster articles, such as Virgo cluster of galaxies and Coma cluster of galaxies. --Reuben 01:17, 17 August 2006 (UTC)

text: The merged version looks great, by the way.  Thanks for taking care of that.  --Reuben 03:55, 17 August 2006 (UTC)
replies: text: Thanks. If no one makes an issue of it feel free to move the artice to "Bullet cluster of galaxies" when appropriate. I recommend a week from now as being appropriate. Should "Bullet Cluster" or "Bullet cluster" be used within the article? I don't know. But if "Bullet Cluster" is correct for within the article then "Bullet Cluster of galaxies" is more corrct than "Bullet cluster of galaxies". I think. WAS 4.250 05:51, 17 August 2006 (UTC)

text: Hmm, actually I tend to agree that "Bullet cluster" sounds better, and I'm used to hearing it always called just the "bullet cluster."  Maybe the other cluster articles should be moved?  I suppose I could take a look and see if there's been a discussion about galaxy cluster naming. --Reuben 16:50, 17 August 2006 (UTC)
replies: text: The general rule on naming articles is to use the most common name; to use what someone would type in the search box as their first guess; to use what will most often be used in other articles to refer to it; to use what our sources and the general media call it. The most common exceptions that I'm aware of are the use of technically correct names especially in biology due to accuracy concerns, the use of disambiguation elements in titles, and the use of NPOV elements in titles with strong emotional ties. WAS 4.250 00:05, 18 August 2006 (UTC)
thread_title:  Merge with Bullet cluster of galaxies 

message: * CXO: NASA Finds Direct Proof of Dark Matter (NASA Press Release 06-297) August 21, 2006
* CXO: 1E 0657-56: NASA Finds Direct Proof of Dark Matter (
* CXO: Bedeviling Devil's Advocate Cosmology (The Chandra Chronicles) August 21, 2006
* NASA: A Matter of Fact (Charlie Plain) 08.21.06
* NASA: NASA Finds Direct Proof of Dark Matter (NASA Press Release 06-297) Aug. 21, 2006
* ScienceDaily: NASA Finds Direct Proof Of Dark Matter (NASA) August 21, 2006
*  This Week's Finds in Mathematical Physics (Week 238) (John Baez) August 16, 2006
* Dark Matter Exists 11:52 am, August 21st, 2006
* arXiv: A direct empirical proof of the existence of dark matter (Marusa Bradac) Sat, 19 Aug 2006 17:51:03 GMT
* arXiv: 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
:some links, I'll snip this down to an external links section for the article.  Zzzzzzzzzzz 08:07, 22 August 2006 (UTC)
thread_title:  External links 

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thread_title:  External links modified 

message: It's hard to relate the x-ray image to the HST image eg as the HST image has no scale. A combined image might help - eg the NASA one at  places the DM centers just outside the 2 x-ray centres. Not clear in any of the images which galaxies are considered in the 'bullet cluster(s)'.  A clearer image of the ~40 galaxies in the cluster(s) would be helpful. (Some of the galaxies may be much more distant background ?) - Rod57 (talk) 21:28, 10 February 2017 (UTC)
thread_title:  How relate the x-ray image to the HST image 

message: Not clear which of the ~40 galaxies has had their distance determined (and if all distances based just on overall galactic red-shift from reddening or shift of spectral lines ?) How has the distance of the x-ray source been determined ? - Rod57 (talk) 21:21, 10 February 2017 (UTC)
thread_title: How were all the distances determined