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Is Dark matter homogeneous in Universe?

  1. Jul 16, 2015 #1
    Is Dark matter homogenenius in Universe ? I dont think so but I dont know any idea about it.
    Thank you
     
  2. jcsd
  3. Jul 16, 2015 #2

    Bandersnatch

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    No, it isn't. It clusters like normal matter, but in more diffuse distribution due to the lack of dissipative interactions. You get, for example, halo-like structures around galaxies.

    Try googling 'dark matter distribution', and you'll get plenty of hits to scientific papers, popular articles and images mapping the distribution. IIRC, some of the free planetarium software out there also allows viewing DM distribution as it's known today (Digital Universe should have that functionality, I think).
     
  4. Jul 16, 2015 #3

    Orodruin

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    The funny thing is that dark matter structure was likely responsible for the large scale structure of baryonic matter through the formation of gravitational wells in the early Universe. Without dark matter, there would be significantly less structure on large scales.
     
  5. Jul 16, 2015 #4

    phinds

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    Just to add to what has already been said, on VERY large scales, dark matter, like regular matter, is taken to be homogeneous, or more technically appropriate, "isotropic" but not in scales such as galactic clusters (which can be REALLY REALLY big by human standards)
     
  6. Jul 16, 2015 #5
    I am talking about very very large scales.Not small distances.Is phinds idea true ?
     
  7. Jul 16, 2015 #6

    phinds

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    Do you think I"m making it up???

    How large is "large" to you?
     
  8. Jul 16, 2015 #7
    Like universe radius distance.
     
  9. Jul 16, 2015 #8

    phinds

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    The universe HAS no "radius" so that doesn't make any sense.

    If you mean the radius of the observable universe (as opposed to "the universe") then yes it absolutely is isotropic.
     
  10. Jul 16, 2015 #9

    Bandersnatch

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    Here's a 1 billion ly across mapped region of the universe.
    Sideshear.jpg
    (taken from: http://www.cfht.hawaii.edu/News/Lensing/)
    Brighter regions are more dense concentrations.
    You can see that while a filament-like structure is still visible, it is approximately homogenous - there are no clearly defined voids and overdense regions. You can easily extrapolate this to an even large scale.
    The bottom line is: both dark and visible matter are approximately homogeneous on large scales.

    And once again, google is your friend. That picture took maybe 5 seconds to retrieve.
     
  11. Jul 16, 2015 #10
    Isotrophic ok What about homogeneius ?.Or Isotrophy universe makes also homogeneius ?
     
  12. Jul 16, 2015 #11

    phinds

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    You'll have to define your terms. The sand on a beach seems VERY homogenous looked at from a distance but if you hold a few grains in your had it doesn't look homogeneous at all.
     
  13. Jul 16, 2015 #12
    I am talking about large scales.

    In the the universe ,dark matter distrubition homogeneius and isotrophic at the scale of observable universe radius ?
     
  14. Jul 16, 2015 #13

    phinds

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    You STILL have to define what YOU mean by "homogeneous". How much granularity is OK to still call it homogeneous?
     
  15. Jul 16, 2015 #14
    At least Homogeneius like the baryonic matter distrubition
     
  16. Jul 16, 2015 #15

    phinds

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    Yes, it is as isotropic as normal matter. They tend to go together at roughly the same ratio (about 5:1) in clumps we call galaxies.
     
  17. Jul 16, 2015 #16

    Bandersnatch

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    @phinds: be mindful of the terms you use. Homogeneity and isotropy are not synonymous, even though the large-scale distribution of dark as well as baryonic matter satisfies both.
     
  18. Jul 16, 2015 #17

    phinds

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    Right ... that's why I've tried to stick with isotropic and have encouraged the OP to define and understand his terms and I have been specific about how I am using "homogeneous" (see post #11)
     
  19. Jul 16, 2015 #18
    Thank you again.
     
  20. Jul 17, 2015 #19
    Could you help me here? I am not interested in an image. I would like to have access to concrete data. Thanks!
     
  21. Jul 17, 2015 #20

    Bandersnatch

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    Follow the link below the picture.
     
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