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Mass of a galaxy without dark matter and with dark matter

  1. Apr 25, 2015 #1
    I am curious about mass of a galaxy without dark matter and with dark matter.I searched but I couldnt found.I ll be happy If you help me.

    Thanks
     
  2. jcsd
  3. Apr 25, 2015 #2

    phinds

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    Well, without dark matter there most likely would not BE any galaxy. although DM does not "clump" the way normal matter does, it has somehow accumulated into cosmologically massive blobs that then attract regular matter through gravitational attraction and the regular matter clumps into stars and planets and dust and the whole mess is a galaxy.

    So asking what a galaxy would be like without the dark matter is a bit like asking how well someone could sing if they had no vocal chords.
     
  4. Apr 25, 2015 #3
    Without dark matter I mean without dark matter mass my fault I forget mass
     
  5. Apr 25, 2015 #4

    phinds

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    Yes, that is exactly what I was talking about.
     
  6. Apr 25, 2015 #5

    mfb

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    How does that change the question?

    For an existing galaxy, you can ask how much visible and how much invisible mass there are. The answer depends on the galaxy and the radius you consider (galaxies do not have sharp edges, especially in the dark matter distribution), but there are many galaxies where numbers are available online.
     
  7. Apr 25, 2015 #6

    wabbit

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    I think the ratio of dark matter to matter is about the same in a typical galaxy (DM halo included) as the overall ratio of 85:15 but I could very well be wrong.
     
  8. Apr 25, 2015 #7

    phinds

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    The rabbit ? WRONG ? Not very likely :smile:
     
  9. Apr 25, 2015 #8

    wabbit

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    Don't joke about the poor rabbit :) he's still recovering from almost loosing his legs in a black hole:smile:
     
  10. Apr 25, 2015 #9
    Is that right isnt it 85/15
     
  11. Apr 25, 2015 #10

    Vanadium 50

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    There exist both DM-rich and DM-poor galaxies.
     
  12. Apr 25, 2015 #11

    phinds

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    do you not understand that 85:15 IS 85/15 or are you making a joke?
     
  13. Apr 25, 2015 #12

    phinds

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    I TOLD you to stay away from those things !
     
  14. Apr 25, 2015 #13

    wabbit

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    Yes mom, I won't do it again, promise:)
     
  15. Apr 25, 2015 #14

    wabbit

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    I was wondering about that, or something related rather - in galaxy collisions the matter tends to coalesce into a single galaxy after a while due I believe to some kind of friction - but with high enough collision velocity it seems that (some part of) the dark matter halos could just move through each other and continue on their way. If that does happen, not only would we be left with a DM poor merged galaxy, but also with stray haloes of dark matter zooming away without much matter left in them . Is that something that happens and if so do we see such stray halos (through lensing or other means)?
     
  16. Apr 25, 2015 #15

    mfb

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    Well, there are objects like the bullet cluster where the distribution of dark matter differs significantly from the distribution of gas.
    Stars also don't have much friction, so a complete separation of visible and dark matter would be odd.
     
  17. Apr 25, 2015 #16

    wabbit

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    Thanks, I thought "some kind of friction" arising from matter-matter interaction (gas clouds maybe?) played a role in the merger process - but you re saying it's minor and essentially gravitational effects alone explain the process, did I get that right?

    And yes I was thinking of the bullet cluster - though I don't recall seeing mention of stray halos escaping in that case, so I was freely extrapolating - perhaps a little too far : )
     
  18. Apr 25, 2015 #17

    phinds

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    Actually, I think the dust interactions DO contribute an effect, it's just that stars/planets are so far apart that THEY don't hit each other.
     
  19. Apr 26, 2015 #18
    Yeah I understand it like that
    Its not 85/15 then what it is.
     
  20. Apr 26, 2015 #19
    I was watching House and there House said dark matter makes galaxies 6 times bigger mass.And I am curious about is that same for every galaxy ? Example a galaxy mass is m without dark matter.But with dark matter 6m.Is that true for all galaxies ? (85/15 near to 6 so I made a connection)
     
  21. Apr 26, 2015 #20

    phinds

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    Which part of post #10 did you not understand?
     
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