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Thread: Gallaxy Colliding

  1. #1 Gallaxy Colliding 
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    Hi,

    Here what I know (or think I know) about the universe and his expansion.

    First, the universe is in expansion, and it's not slowing down. That's break the logic from gravity: the universe should be slowing down. To explain this phenomenon, we conclude that there is more matter than we can see. We called it Dark matter.

    Second, the expansion is in the way that from any point in the universe it looks "the same", like we are in the "middle". It can be compared to a continuously inflated ballon and the galaxies are on the "edge" of the balloon.

    So, I suppose that from the big bang and from now, the universe "has always been in expansion".

    Question #1 : How the matter combine hydrogen in "clouds" and created stars if from the start to today the universe is expanding, meaning every single particules going further from each other ?

    Question #2 : How can galaxy can collide ?

    Sorry if my question are "basics". If you could help me find book or articles that can explain to me how it works it would be appreciated.


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  3. #2  
    Quagma SpeedFreek's Avatar
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    Quote Originally Posted by Havarem View Post
    Hi,

    Here what I know (or think I know) about the universe and his expansion.

    First, the universe is in expansion, and it's not slowing down. That's break the logic from gravity: the universe should be slowing down. To explain this phenomenon, we conclude that there is more matter than we can see. We called it Dark matter.
    Hi there!

    You are mixing up dark matter with dark energy here.

    To explain the phenomenon that the expansion is accelerating rather than slowing down, we use dark energy, which works against gravity in the same way as a cosmological constant. The "more matter than we can see" explanation, i.e. dark matter, is required to explain the rotation curves of galaxies.

    Quote Originally Posted by Havarem View Post
    Second, the expansion is in the way that from any point in the universe it looks "the same", like we are in the "middle". It can be compared to a continuously inflated ballon and the galaxies are on the "edge" of the balloon.

    So, I suppose that from the big bang and from now, the universe "has always been in expansion".
    Agreed.

    Quote Originally Posted by Havarem View Post
    Question #1 : How the matter combine hydrogen in "clouds" and created stars if from the start to today the universe is expanding, meaning every single particules going further from each other ?
    Gravity causes regions with higher concentrations of matter to converge and form structures, whilst distances increase in regions with lower concentrations of matter. The lumpier regions get more lumpy, whilst the less lumpy regions get even less lumpy.

    Quote Originally Posted by Havarem View Post
    Question #2 : How can galaxy can collide ?
    If two galaxies form relatively close to each other, gravity will attract them towards each other. At further distances, where the attraction of gravity is less, there comes a point where the universal expansion beats gravity and galaxies become further apart.

    Have a look at the following PDF article, from Scientific American (the first page is blank, by the way..)

    http://www.mso.anu.edu.au/~charley/p...DavisSciAm.pdf


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  4. #3  
    Reptile Dysfunction drowsy turtle's Avatar
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    Hey Havarem, welcome to TSF

    Quote Originally Posted by Havarem View Post
    Question #1 : How the matter combine hydrogen in "clouds" and created stars if from the start to today the universe is expanding, meaning every single particules going further from each other ?
    The very fact that this did happen means we can conclude that the universe isn't completely homogenous. Small variations in the amount of matter from place to place probably led to the formation of black holes in the early universe, which then drew in more matter later on to form galaxies.

    Quote Originally Posted by Havarem View Post
    Question #2 : How can galaxy can collide ?
    I don't think this is a common phenomenon, but galaxies are arranged into groups, and further into 'supergroups', before the universe becomes homogenous on larger scales. Within these groups, galaxies might collide, while still moving away from the rest of the universe. Groups of galaxies might even collide, but don't quote me on that
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    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  5. #4  
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    Thanks guys,

    I'll take a look at the PDF.
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