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Empty Part of the Universe?

  1. Sep 5, 2007 #1
    I know that astronomers have found things like this before, but to find an empty part of space this big really makes you wonder.... My question to you all is, what are your theories on why there is emptiness in certain parts of space?
  2. jcsd
  3. Sep 6, 2007 #2


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    Since space has 'stuff' randomly scatter through it - empty generally means something has moved through a volume and swept up anything there.
    Could be a galaxy or a cluster of galaxies formed and moved through the volume collecting up any material.

    Larger areas may have more cosmological explanation - whatever originally caused matter to clump together into galaxies would equally have left emptye volumes where that matter came from.
  4. Sep 6, 2007 #3
    I've read that galaxies like to gather in sheets or clusters. I would say it's empty there because there's gravity from the neighborhood of galaxies next to the empty space. Maybe the big bang wasnt perfectly distributed in all directions. It missed a few spots.
  5. Sep 10, 2007 #4
    Let's not forget that what appears to be empty might in fact be teeming with things we simply can't see. Perhaps it's so full of the invisible stuff there isn't any room for Galaxies (although I reeeaaaalllllllyyy doubt that), such as dark matter.

    One can tell by the way that matter appears in clumps such as Galaxies that the big bang didn't offer an even spread of all the matter, so I guess a huge void isn't out of the question or anything.
  6. Sep 10, 2007 #5


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    It depends on what you mean. If you're referring to "voids", then the emptiness refers to a relative lack of matter compared to the universal mean on ~1-100 Mpc scales. However, voids, can still have galaxies, dark matter, gas...almost anything that can be found in clusters, it's just more sparsely distributed.

    The origin of these voids is related to the way in which matter undergoes gravitational collapse as the universe expands. The fluctuations put in place early on tend to grow with time and overdense regions tend to attract matter from underdense regions, emptying them out. By the present day, you get a cellular structure, with walls and filaments sitting at the edges of massive voids.
  7. Sep 10, 2007 #6


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    Nice post, Nick
    glad to see you back around more.
    Last few months were finishing up thesis time, I gather.
    Hope everything went well and it's on to postdoc.
    Last edited: Sep 10, 2007
  8. Sep 10, 2007 #7


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    I did some research and them some math, and I figured that this void is about twice the size of the next largest one known. (there are several other threads on this, and my reasoning is in noe of them, somewhere)
    I read that this area is thought to be fairly devoid of dark matter, based on the behavior of objects around or nearby.
    It also strikes me that the void is 6-8 billion ly away, meaning that we are seeing it as it existed six or eight billion years ago, when the universe had not expanded nearly as far as it has today. It's one thing to find such a very large void, but to find it in such a very small universe only compounds the wonder!
  9. Sep 11, 2007 #8
    I was thinking the same thing. If it was 1 Gly across 6-8 Glys ago, what would be its size today given the expansion rate?
  10. Sep 11, 2007 #9


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    A volume 6-8 GLy ago was at z = 0.6-1.1 and thus 1.6-2.1 times smaller than today, if we only take into account expansion. However, voids expand not only due to expansion of space but also due to gravitational collapse of matter between them. I don't know how to estimate this.
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