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Presence of Dark Matter

  1. Aug 20, 2015 #1
    As observed in published space maps, I have noted that dark matter is present only in those region which already have visible mass around them. Is this really a fact or just my wrong belief?
  2. jcsd
  3. Aug 20, 2015 #2


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    They are associated. In theory, DM because there is more of it, clumped first. And concentrations of DM helped to pull ordinary matter (OM) together by its gravity, leading to regions of higher than average density of OM.

    So there is a correlation---regions where there is higher than average density of DM tend also to have pockets of higher than average density OM---not just visible in the form of stars but also gas, dust etc.

    But the correlation wouldn't be absolute. there would be regions containing SOME dark matter, maybe just at very low density, in which no significant amount of OM had collected.

    I'd be interested to see some of those maps, if you happen to have links to some online ones. DM is hard to detect except where it is in unusually high concentration and there are steep gradients in density that cause an optical distortion of the background (gravitational lensing). I wouldn't expect most DM to register that way---it would be too uniformly spread out. Maybe they just don't show DM where it is below a certain density. Anyway I'm wondering how the maps were made.
    Last edited: Aug 20, 2015
  4. Aug 20, 2015 #3
    'Dark matter' is now understood to fill what would otherwise be considered to be empty space.

    'Cosmologists at Penn Weigh Cosmic Filaments and Voids'

    "Dark matter ... permeates all the way to the center of the voids."

    'No Empty Space in the Universe --Dark Matter Discovered to Fill Intergalactic Space'

    "A long standing mystery on where the missing dark matter is has been solved by the research. There is no empty space in the universe. The intergalactic space is filled with dark matter."
  5. Aug 21, 2015 #4
    That means my assumption is partially correct or wholly:smile::smile:
  6. Aug 21, 2015 #5
    Where DM is most dense it has assisted ordinary matter to become more dense.
    It's not so much a correlation as an inevitable consequence of gravity pulling matter together regardless of what sort of matter it is.
  7. Aug 24, 2015 #6


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    It is also quite hard to observe DM in the absence of stars in the vicinity with which one can measure either dynamics compared to a no DM hypothesis, or use lensing to measure it. It would take an incredible coincidence to have conditions right to observe DM effects if there was a random DM only clump in the middle of a large void.
  8. Sep 2, 2015 #7
    Dark Matter mainly exists in the halos of galaxies meaning their outer ring and the fact that it exists in galaxies is very important and is one of the reasons the stars in galaxies do not fly away due to the rational velocities of the galaxies, so that extra mass holds it together.
  9. Sep 2, 2015 #8
    I prefer to think of it that galaxies exist in dark matter. There is much more dark matter than their is matter.
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