Talk:Spiral galaxy

message: How is it that something that seems so simple can be so complicated? All of our lives are in this galaxies hands and the is nothing that we can do but sit and wait for somthing to happen all over again.--207.12.157.2 15:38, 6 September 2005 (UTC)
replies: text: Wikipedia is not for personal feelings or thoughts.  — Preceding unsigned comment added by 188.39.71.98 (talk) 14:35, 27 November 2018 (UTC)
thread_title: Simple and complicated?

message: I'm having some trouble with the proposed explanation for spiral structure in the article, "The first acceptable theory was devised by C. C. Lin and Frank Shu in 1964. They suggested that the spiral arms were manifestations of spiral density waves. They assumed that the stars travel in slightly elliptical orbits and that the orientations of their orbits is correlated, i.e. the ellipses vary in their orientation (one to another) in a smooth way with increasing distance from the galactic center." The diagram illustrates a sequence of concentric ellipses with differing orientations, all centered at the galactic center, and postulates these elipses as the orbits of stars in the galaxy: that the stars orbit in elipses *centered* at the galactic center. But shouldn't eliptical orbits aroung the galactic center have the galactic center at one focus, rather than at the center? Or is the fact that there is a distribution of mass over the whole galaxy, and not just at the center the cause? In any case, I found this point confusing, and I think it merits an explanation. Althai 22:14, 3 October 2006 (UTC)
replies: text: The picture is a somewhat oversimplistic explanation for spiral arms in galaxies.  For one thing, if you simply imagine stars orbiting on fixed elliptical orbits like the one shown then it implies a stationary spiral pattern.  In fact, the spiral pattern propagates around the galaxy.  The ellipticities are also highly exaggerated in the figure - in reality the density contrast in spiral arms is very low and the orbits nearly circular.  You're right about the fact that elliptical orbits should be focussed on the centre of mass and that you have to consider how mass is distributed throughout the galaxy.  The last point is key, because the stars in the disk orbit in their own combined potential of their own self-gravity.  This is completely different to, say, a planet orbiting a star.  Self-gravitating systems are prone to resonant oscillations and it is this that leads to the formation of spiral arms.  The whole theory of orbits is very complicated - I've studied it and I still don't understand it. Cosmo0 09:05, 21 September 2007 (UTC)

text: The sphere of influence of a black hole (and even a black hole binary) is very small compared to an entire galaxy, so it doesn't explain the spiral structure in galaxies.  Which is not to say that some of what you say isn't true in some circumstances: orbiting binaries can cause spiral-like structures, e.g. the tidal arms thrown off by 2 merging galaxies. Cosmo0 09:09, 21 September 2007 (UTC)
thread_title:  Explanation for Spiral Structure 

message: Agree. Merge into a historical section and make spiral nebula redirect here. --IanOsgood 16:09, 4 June 2007 (UTC)
replies: text: Done. Cosmo0 19:06, 21 September 2007 (UTC)
thread_title:  Merge [[spiral nebula]] 

message: In a recent paper published in Proceedings of The Royal Society A, Charles Francis and Erik Anderson presented a model of spiral arms, matching observations and showing how the mutual gravity between stars causes orbital rosettes to align so as to form logarithmic spirals. Density wave theory is shown to be based on elementary mathematical mistakes and incorrect physics, and makes observationally incorrect predictions about stellar motion (stars do move along the arms, and orbits are not nearly circular). I have editted this article accordingly RQG (talk) 07:25, 25 August 2009 (UTC)
replies: text: I'm gravely concerned that a user whose name RQG matches rqgravity.net, the site of the author of a theory that is not widely accepted (despite having made it into a peer review journal). The material should not be stated as fact until this hypothesis is widely accepted, and ideally shouldn't be in the article at all. 87.194.227.22 (talk) 23:28, 28 August 2009 (UTC)

text: I'd be surprised if it were widely accepted when the animation of the model in question clearly doesn't resemble the actual kinematics of spiral galaxies. I've had bad experiences of edit wars in wikipedia and I'm not going to invest time on this but perhaps a more regular wikipedia editor would care to contact a recognised expert for an opinion. Arguing that this material should be in because other material is in wikipedia is also a poor argument. Either better justify this, or argue for the deletion of the material that offends you. 87.194.227.22 (talk) 08:47, 29 August 2009 (UTC)

text: i have deleted the entire self promotional paragraph touting the theories of "postgraduate student" grand. a conference presentation is *not* a peer reviewed publication, and while i decline the savory opportunity to declare RQG's theories to be crank science, it *is* a well rehearsed crank science tactic to claim that conference proceedings, invited papers or other forms of occasional speech are peer reviewed ("in so far as one can tell"), then to argue and niggle the point with a typically overworked wikipedia editor. the obvious reason a presentation is not a peer reviewed publication is that the content delivered ex tempore need not be the content submitted for approval, and the content claimed after the fact need not be the content delivered, and there need not even be anyone in the room at the time the "presentation" was made. a peer reviewed article has been explicitly read, vetted and commented upon by experts in the field, and their dialog with the author supervised by a competent editor: the fact of publication requires that process and stands as its surety. RQG can claim none of the above for his ideas, and his claim above that Shu makes "elementary mistakes" in physics or mathematics, or that peer reviewed science is really only, when you think about it, a different kind of crank science, is so fatuous as to be comical. deleted with prejudice. Macevoy (talk)  —Preceding undated comment added 20:58, 9 August 2012 (UTC)

text: I'm aware of the potential for a misleading illusion but it's as plain as day that the outer stars are moving more slowly than the inner ones. There's no clear discussion of the rotation curve in the article, no match to anything other than local stellar data and radio data for the Milky Way, with no attempt made to fit to other galaxies. Note also that I never referred to this theory as crank and it may well turn out that it can be made to work but this is an important article which has had this hypothesis dropped into it in a manner that suggests it as fact by an author of the paper, presumably. 87.194.227.22 (talk) 08:09, 30 August 2009 (UTC)
thread_title:  New Explanation for Spiral Structure 

message: Is this really considered to be a legitimate competing theory or is it something proposed by a handful of scientific outliers? If the former, then why isn't there more information, as there is with the density wave model? Also, why is there a whole sub-page dedicated to this theory that only consists of three sentences? 
If it's a genuine accepted competing theory, then it seems to me that the sub-page should be deleted and that info should just be folded into the main article, which could handle an extra three whole sentences. If it's not accepted by the scientific community at large then I think it should be deleted. 
Shoeless Ho (talk) 16:34, 12 January 2012 (UTC)
thread_title:  SSPSF model 

message: "Together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in the local Universe."
Why does this statement group irregular and spiral galaxies together, when they seem quite different? What proportions of that 60% are attributable to each type? Without these details, the statement seems pointless and confusing.  — Preceding unsigned comment added by 24.213.20.170 (talk) 17:59, 9 January 2014 (UTC)
thread_title:  Irregular Galaxies 

message: The remark, under "Density wave model", about a bogus diagram, needs resolving.  — Preceding unsigned comment added by Racialism123racialism123racialism (talk • contribs) 16:56, 26 February 2014 (UTC)
thread_title:  Needs resolving 

message: I was reading a 19th century book on batteries (Storage of Electrical Energy by Gastone Plante) and came across speculation about the nature of spiral nebulae. His speculations were not correct, but I was curious to know at what point it became known that spiral nebulae were in fact galaxies, i.e. I wanted to know the history of an obsolete theory, I did not want to read about current theory that I'm already well aware of, so I suggest that redirect was ill judged - the current article does not discuss the subject matter I was redirected from. My second problem is that this article begins by claiming that spiral galaxies were "originally described by Hubble in 1936". If we accept that spiral nebulae and spiral galaxies are essentially the same thing (implied by the redirect?), just explained differently, then that opening statement is clearly not true, otherwise Plante writing in the mid-1800's could not have known about them. At the very least this statement needs to be clarified.  — Preceding unsigned comment added by 31.48.1.234 (talk) 09:40, 1 August 2014 (UTC)
replies: text: More information is available at Galaxy#Distinction from other nebulae. I'll sort out the redirect and related stuff later today. HTH Paradoctor (talk) 12:27, 1 August 2014 (UTC)
thread_title:  Spiral Nebulae - Invalid Redirect? 

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thread_title:  External links modified (January 2018) 

message: I propose that Gravitationally aligned orbits be merged into Spiral galaxy. The reasons are as follows:
*Former, athough related to spiral galaxies, is largely a summary of a research paper and does not provide any context of the subject. How can this be notable enough to have a separate article?
*Title is misleading as article body is focused on dynamics of spiral galaxy arms, while title "Gravitationally aligned orbits" may mean any orbits in space.
*No sources other than primary source are given.
*Lead is terrible. This statement From observations of the motions of over 20,000 local stars (within 300 parsecs), and using numerical simulation, Charles Francis and Erik Anderson have shown that, contrary to conventional wisdom, stars tend to move along a spiral arm........, is like advocating for the mentioned authors.
*Moving it to Spiral galaxy would provide context to material discussed in "Gravitationally aligned orbits", and if secondary sources can be found, it can potentially be a valuable addition to Spiral galaxy article.
*I was not sure if deletion nomination would be appropriate in this case. 
Thanks --UbedJunejo (talk•cont) 18:14, 6 March 2018 (UTC)
replies: text: Just took a look and I would suggest deletion of that article. As you pointed out, the Wikipedia article is basically a summary/advertisement for a single journal article. There is no evidence that this journal article is noteworthy. In ADS it has just 15 citations, several of which are self-citations. This doesn't even deserve to be a subsection of the spiral galaxy article. At most, maybe a single sentence could be included describing some key result from this paper, but I wouldn't even go that far unless there was some evidence that this was a noteworthy or influential paper or that any results in this paper were broadly recognized as being important for spiral galaxies. I don't think there is evidence that the information in this article is important enough to merge into the general article on spiral galaxies. Aldebarium (talk) 19:14, 6 March 2018 (UTC)
replies: text:  Yes, Google Scholar gives about 20 results, of which some 17 are unique. Of those 17, about a third are self citations. Other cite this paper only in other regards and DO NOT mention this new theory, apart from a book, which prefers old density wave theory. I was reluctant to nominate it for deletion because, to my mind, it could have been presented as an alternative theory. If other also find deletion a better option, I will concur. --UbedJunejo (talk•cont) 20:23, 6 March 2018 (UTC)
thread_title:  Merger Proposal 

message: The article mentions 2 theories, density wave and SSPSF.  However, only the former then gets many paragraphs of further explanation, which is at least stylistically unbalanced.  Such a long explanation would be better moved to an article of its own -- which already exists!  (So why is it taking up so much space here?) Jmacwiki (talk) 05:38, 14 April 2018 (UTC)
thread_title:  Pattern formation theories 

message: Ref. #9 (Ibata et al.) relates to the unexpected planar structure of satellite galaxies observed in just 2 galaxies [and recently a 3rd].  This article does not state any connection between satellites and the spheroid, nor is it clear that it should.
FWIW, the research finding may or may not be important for theories of gravity (as one of the authors is quoted as believing), but this article is not the appropriate place to make that case.
Comments before removing that sentence and reference? Jmacwiki (talk) 20:33, 22 April 2018 (UTC)
replies: text: Agreed, it's ok to remove that. This article isn't the best place to cover that particular topic. Aldebarium (talk) 00:16, 23 April 2018 (UTC)
replies: text: Done. Jmacwiki (talk) 16:59, 29 May 2018 (UTC)
thread_title:  Satellites vs. flatness? 

message: I would like to rewrite the section about "Origin of the spiral structure". Perhaps, moving more details to the Density wave theory page.
This section requires clean up. Right now, some of the information is simply wrong, and some "alternative" theories included are not mainstream at all. 
What is wrong:
* The figure of multiple eclipses is actually about "kinematic wave" suggested by Lindblad (see Bertin and Lin 1996, Figure 2.4, page 72), rather than the Lin-Shu theory. In Lin-Shu theory, the orbits and the spiral pattern are fixed only in a particular rotating frame (pattern frame).
Theories should be removed from this page:
* SSPSF theory is nowhere a mainstream theory. No mention in the academic literature.
* Gravitationally aligned orbits: As discussed above, this theory is not well accepted.
Wklee4993 (talk) 18:42, 23 February 2019 (UTC)
replies: text: That would be a great contribution. Thanks in advance for investing some effort into this article. Aldebarium (talk) 18:58, 23 February 2019 (UTC)
thread_title:  Origin of the spiral structure 

message: isnt the new black hole picture a picture of a super massive black hole? GlowZoe (talk) 06:56, 11 April 2019 (UTC)
replies: text: what do you mean User:Hamterous1 (discuss anything!🐹✈️) 00:10, 24 April 2024 (UTC)
thread_title:  The new picture