Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A rudementary question on dark matter

  1. Jan 26, 2013 #1
    I think that there is mass associated with all dark matter in the universe and this mass is much greater than the total mass of the stars in a particular galaxy.

    Now, if I were to classify the mass into two categories :
    1. visible
    2. invisible

    How would I carry that out ?

    Is dark matter invisible mass or would it be counted as visible mass ?
  2. jcsd
  3. Jan 26, 2013 #2
    let me rephrase that, is dark matter visible to the eye ?

    Does it emit e.m radiation in the visible region of the spectrum ?
  4. Jan 26, 2013 #3
    "dark matter" does not emit radiation in the visible region or any other region of the EM spectrum...otherwise we would be able to detect it, and not just theorize its existence. the best evidence of the existence of dark matter is indirect - that is, we can't detect dark matter directly, but we can see its effects on ordinary matter. take spiral galaxies for instance - surely their inner regions orbit their respective galactic centers faster than their outer regions...and yet the outer regions still appear to orbit their respective galactic centers much faster than their detectable masses suggest. and so some scientists theorize that there is a substantial amount of "dark matter" in those outer regions (that cannot be seen by any ordinary means of detection) that provide the additional gravity necessary to account for the faster-than-predicted orbits of the outer regions of spiral galaxies about their respective galactic centers.

    so your hypothesis that there is mass associated w/ dark matter is in line w/ dark matter theory, b/c even though it does not radiate anywhere in the EM spectrum, its gravitational effects can be detected.
  5. Jan 26, 2013 #4
    The existence and location of dark matter can be inferred by gravitational lensing. It is one of the best ways we have to locate it but even then it's not easy. I do remember a team of astronomers created a map of the dark matter, if I find it ill link it. However dark matter is still classified as invisible matter in your question. Visible matter are things like planets, stars, galaxies, etc. Dark matter is its own form of matter and does have mass and it is predicted to be much larger than the mass of what we can see.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook