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GALAXIES - what was 'extra' so visible matter was presumed missing?

  1. May 18, 2013 #1
    Dark matter is presumed.... to balance the sums... as visible matter doesn't work out (apparently) to a high enough value.....

    .... What part of the calculations was evaluated as being too high.... to warrant the need for more matter to be 'somewhere'.

    Thanks for thoughts
  2. jcsd
  3. May 18, 2013 #2


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    The rotational speed of the stars in the outer reaches of the galaxy is WAY off based on just the normal matter in the galaxy ... There has to be a huge amount of mass in addition to normal matter and that's how dark matter was inferred. It has been further verified by gravitational lensing.
  4. May 18, 2013 #3
    OK thanks, 'phinds'....

    so..... the rotational speed of stars in the outer reaches = faster than the quantity of mass, seen to be around.... (providing gravitational force) to balance the sums.... to hold them in their place, as observed.

    * ... anyone know established papers with these sums?... (who concluded missing visible matter)

    I've found another topic on these boards which is most interesting and have placed the link... should anyone else just reading this thread, wish to also consider:
    Rotational Speed:

    * ... is it established, what gives a galaxy (spiral one).... it's rotational speed
    * ... is there a top paper on rotational speeds (spiral galaxies)

  5. May 18, 2013 #4
    Here is a decent article though its more a review paper on LCDM measurements.


    What your interested will be better answered here.


    It will cover the effect dark matter has on rotation curves better
    along with this page
    Last edited: May 18, 2013
  6. May 18, 2013 #5
    Thanks for links, 'Mordred'....

    Your links are helpfull.... the first article one especially... rotational velocity in relation to radius distance etc

    I've found another topic on these boards which is most interesting and have placed the link... should anyone else just reading this thread, wish to also consider:
    simple explanation for rotation of spiral galaxy:

    * ... am increasingly interested in honing in on the specific most established (agreed so far) actual cause of the velocity itself..... in the rotation (for a spiral galxy)

  7. May 18, 2013 #6

    You probably know MOND. The author Moti Milgrom invented the possibility to explain the rotation curves with a modification of newtonian dynamics as an alternative to DM. As the author says himself, it is a phenomenological observation only. But it is still in use! This year a team from germany/Bonn explained the bahaviour of satelite galaxies with MOND where the DM theory failed. I believe there is invisible mass. But who knows, maybe there is "something" to MOND.

    Original Publication: Milgrom, 1983, The Astrophysical Journal, free from arxiv or google
  8. May 18, 2013 #7
    MOND does provide a good fit to a certain class of gas-rich galaxies. The problem is MOND by *itself* does not seem to work in all situation: fitting CMB data for example. For more, see http://blogs.discovermagazine.com/cosmicvariance/2011/02/26/dark-matter-just-fine-thanks/.
    But of course that is not saying modified gravity is ruled out!
  9. May 19, 2013 #8
    while MOND does have good results at the smaller dwarf galaxy scale. It seriously lacks on average galaxy rotation curves.
    Also MOND cannot explain gravitational lenses or early large scale structure formation.
    In some specific examples MOND does work better than LCDM dark matter however thats more due to our lack in our knowledge of dark matter distributions.
    Several MOND articles I have read include dark matter though
    I would have to remember the
    articles and locations of them
  10. May 19, 2013 #9


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    Any MOND theory that requires dark matter defeats the entire premise.
  11. May 19, 2013 #10
    I fully agree Chronos it does contradict the MOND premise.

    That aspect is discussed in this recent LCDM and MOND review of challenges and difficulties faced in both models.

    Coincidentally it will also provide a direction of current researches and challenges in our understanding of the dark sector.
    Further reading can be found via the articles reference papers.
    Some of the reference papers are worth reading.

    The article is also handy in that it covers rotation curves of spiral galaxies. However I will not state which is the most agreed upon
    lol. My opinion is biased towards the LCDM paradigm.

    Last edited: May 19, 2013
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