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Big Dipper Cosmic Ray Hotspot Homogeneity question

  1. Jul 8, 2014 #1
  2. jcsd
  3. Jul 9, 2014 #2

    Chalnoth

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  4. Jul 9, 2014 #3

    Chronos

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    The principles of homogeneity and isotropy [i.e, the Copernican principle] only applies on scales much larger than a galaxy.
     
  5. Jul 11, 2014 #4
    Ultrahigh-energy cosmic rays stem from outside the Milky Way, but are weakened by interactions with the cosmic microwave background radiation — the leftover fingerprint from the Big Bang that kicked off the universe. As a result, 90 percent of the detected ultrahigh-energy cosmic rays originate within 300 million light-years of Earth.

    According to Jui, a separate study currently in progress suggests that the distribution of ultrahigh-energy cosmic rays in the northern sky is related to concentrations of large-scale structures like clusters and superclusters of galaxies.



    The article mentions superclusters of galaxies. Are these big enough to be a concern for homogeneity?
     
  6. Jul 11, 2014 #5

    Chronos

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    No. You are suggesting extragalactic sources which are not proven to be an issue.
     
  7. Jul 11, 2014 #6

    Chalnoth

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    No. Why would they be?

    Some level of inhomogeneity is expected at all size scales. The homogeneous assumption is only ever an approximation.

    It is possible to challenge ##\Lambda##CDM if it can be shown that there are far more extremely large objects in the observable universe than we would expect given that model. But so far such challenges haven't held up under scrutiny.
     
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