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B What's Dark Matter?

  1. Mar 1, 2017 #1
    I and my friend were talking about dark matter. Can anyone define or explain what dark matter is? Link to websites is fine but straight information for the best.
  2. jcsd
  3. Mar 1, 2017 #2


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    Have you looked it up. Done any research at all?

    EDIT: I see you have only a few posts. Perhaps you are under the mistaken impression that this is a Q&A forum where you just ask a question and we spoon feed you an answer. It doesn't work like that. You have to show some effort on you own part. Do some research and then ask specific questions about dark matter if any remain.
  4. Mar 1, 2017 #3

    Mister T

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    Add up the masses of all of the stars in a galaxy and that should give you a good estimate of the mass of that galaxy. Stars glow, and it's the stuff that glows that has mass. For example, almost 100% of the mass of our solar system is the mass of the sun. The planets make an insignificant contribution so that's where we get the idea that it's the stuff that glows that has the mass. (Yes, there are black holes, but there are ways of accounting for their contributions, too)

    We also know that the revolution of our planets is determined by the mass of our sun. If it had more mass the planets would revolve faster. Also, the planets in closer revolve faster.

    If we try to use these two ideas to explain the observed rotation of galaxies, they don't mesh. We're missing about 90% of the mass needed to account for the rotation rates. Since the matter that makes up this mass can't be seen, that is it doesn't glow like the stars do, we call it dark matter.

    I urge you to take phind's advice and do some research on the topic. Let us know if you encounter any information that doesn't make sense to you.

    You can make a long list of possible sources of this missing mass, but one by one you have to cross most of them off the list because they can't get the job done. It's a true mystery.
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