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  1. Jan 14, 2006 #1
    Last edited: Jan 14, 2006
  2. jcsd
  3. Jan 14, 2006 #2

    SpaceTiger

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    Also, check this out:

    New Milky Way Neighbor

    It's an announcement from one of the groups I'm working with. We've found an overdensity of stars in the SDSS survey that, if real, might represent the nearest galaxy to the earth. My roommate is the first author on the paper (Juric et al.).
     
  4. Jan 14, 2006 #3

    Garth

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    Thank you ST - if real, then a low mass galaxy of ~ 106 stars and about 20,000 light yrs across? (Subtends ~300 at 30,000 lgt yrs.) So a very low stellar density galaxy.

    Would it be noticed if further away, and if not then how many more are there out there?

    Garth
     
  5. Jan 14, 2006 #4
    pity i can't subscribe to this. do you know any other stuff that i can subscribe to freely, via e-mail?
     
  6. Jan 14, 2006 #5

    SpaceTiger

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    I don't think it would have been, mainly because a galaxy as sparse as this would have an extremely low surface brightness. Your second question is so far unanswered, but LCDM theorists are trying hard to. An abundance of such galaxies would lead to a possible resolution of the "small-scale structure problem". This arises from the fact that the standard model seems to overpredict the number of small dark matter halos in the vicinity of the Milky Way. If they were present but escaping detection, then there would no longer be a discrepancy.
     
  7. Jan 14, 2006 #6

    SpaceTiger

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    I'm not subscribed either. Are you saying you can't see the article?
     
  8. Jan 14, 2006 #7

    Garth

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    Yes, that was my drift. About ten years ago I heard a presentation of a paper that suggested the inter-cluster voids may in fact be not as deficient in density as they appear but filled with very low surface brightness galaxies that cannot be observed.

    Garth
     
  9. Jan 14, 2006 #8

    SpaceTiger

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    I'm sure that's possible as well. That wasn't work by Michael Vogeley, was it? I know he's big into the voids.

    Fortunately for LCDM, the problems seem to lie in the regimes in which we have the least observational and theoretical certainty. If, instead of "small-scale structure" and "cuspiness" problems, we had "large-scale structure" and "rotation curve" problems, LCDM would be in a lot of trouble.
     
  10. Jan 15, 2006 #9
    well i can... but it's a magazine isen't it? so it's not free. and i can't get it through e-mail.
     
  11. Jan 15, 2006 #10

    SpaceTiger

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    I don't really know, I was just linking the story. I don't subscribe to any pop. sci. magazines or email services, so hopefully someone else can offer some suggestions.
     
  12. Jan 16, 2006 #11

    Nereid

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  13. Jan 16, 2006 #12

    Garth

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    And that story refers to our very own SpaceTiger.:smile: Well done ST!
    So what is the limit on DM is there in our neighbourhood? And does this go anywhere in resolving the dispute over the Cooperstock & Lieu claim?

    Garth
     
  14. Jan 16, 2006 #13

    SpaceTiger

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    I can't say anything about that yet, partly cause it isn't published and partly because I don't have an answer. Here's a decent review of some of the past results:

    Mass Distribution in Our Galaxy


    I doubt we'll check our results with their model.
     
  15. Jan 17, 2006 #14

    Garth

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    No - I didn't expect that you will! The question really is that if you have secondary confirmation of local DM from perturbations on the infalling stars then that would knock the nail on the Cooperstock & Lieu claim, as well indeed on the Milgrom/Bekenstein MOND hypothesis.

    Garth
     
    Last edited: Jan 17, 2006
  16. Jan 17, 2006 #15

    SpaceTiger

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    It's purely a dynamical test, so it wouldn't necessarily help discriminate dark matter from modifications to gravity. It's possible that their theories would give noticably different kinematics in the solar neighborhood, but we would have to do detailed models to say for sure.
     
  17. Jan 18, 2006 #16

    Chronos

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    2015 Award

  18. Jan 18, 2006 #17

    Garth

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    The paper sets out the present enigma: The Pioneer Anomaly cannot be explained by prosaic causes, gas or radiation leakage, and seems to be a real gravitational effect. This is seen in distant Pioneer and Voyager spacecraft, but there has been no correlating effect in the orbits of the outer planets.

    It proposes a search for such an effect in the outer system asteroids/Kepler objects beyond 20AU.

    One feature of the PA that I find intriguing is the magnitude of the PA acceleration is only just larger than the Hubble Acceleration cH, and therefore might well be cosmological in nature.

    Garth
     
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