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B Dark matter stars?

  1. Mar 3, 2017 #1
    ok so this has been on my mind for a while. If the hotter a stars burn or flame the further it goes on the spectrum correct so what if it burned so hot it is literally invisible wouldent that be considered a dark matter then it's a dark matter sun
     
  2. jcsd
  3. Mar 3, 2017 #2

    fresh_42

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    If it emits electromagnetic waves, then we would see it. And a star always does. Even the cold ones, the hottest the more. It doesn't matter whether the emissions are in the visible spectrum or not. This is not what is meant by dark matter. Dark matter is something completely different, and we don't know much about it. To the few we do know belongs the fact, that dark matter doesn't clump and therefore cannot build stars.
     
  4. Mar 3, 2017 #3
    I'm in 8th grade thx still learning love physics and astronomy
     
  5. Mar 3, 2017 #4

    fresh_42

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    You're welcome, and by the way

    :welcome:

    Have fun!
     
  6. Mar 3, 2017 #5

    rbelli1

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    Some very hot very distant astronomical objects are only detectable in the X-ray and gamma-ray spectrum. The visible light they emit is just too feeble to detect from Earth while the higher wavelengths are much stronger.

    Here is one of the beasties we use to see these:

    http://chandra.harvard.edu/

    BoB
     
  7. Mar 3, 2017 #6

    Orodruin

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    It has been speculated that dark stars with a high amount of dark matter inside existed in the early Universe (https://arxiv.org/abs/0705.0521). However, these objects would be very cold and therefore not be detectable as the emitted radiation would be very low frequency. They would be kept from collapsing by dark matter annihilations.

    Note that you cannot make something invisible by heating it. Although the peak of the emission spectrum would shift to unobservably high frequencies, the total emission would increase in such a way that the emission in the visible sector would increase rather than decrease, ie, it would become even brighter. The way of obtaining an object whose EM radiation cannot be seen is to make it cold so that the intensity decreases. Dark matter is a different issue, it does not emitt EM radiation at all (or very very very weakly).
     
  8. Mar 3, 2017 #7

    mfb

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    Hotter objects emit more radiation than colder objects - for every wavelength range.

    We can detect gamma rays without an upper energy limit - at high energies they just get too rare to measure their rate reliably, but if there would be something emitting them often we would easily see it.

    Stars cannot get too hot - otherwise the intense radiation pressure would quickly remove their outer shells, cooling the star.

    We know that dark matter has a different distribution than visible matter. It does not clump together like visible matter does - it cannot be in star-like objects (at least not most of it).
     
  9. Mar 3, 2017 #8

    Bandersnatch

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    The hotter the star, the further on the spectrum is the peak radiation intensity. For any wavelength, intensity increases with temperature. It's just that as stars get hotter, larger proportion of light is in the shorter wavelengths, making the star look bluer.
    Below is the black body spectrum, which closely approximates stellar output:
    720px-Wiens_law.svg.png
    As you can see, it 'leans' to the left with increasing temperature (as described by Wien's displacement law). You can imagine a body so hot, that its peak wavelength is way in the gamma range. It would still look blue, since that's where the most intensity in the visible range (~400-800 nm) would be radiated.

    (edit: so many ninjas! ;) )
     
  10. Mar 4, 2017 #9
    Or hot and small. Such as neutron stars.
     
  11. Mar 5, 2017 #10
    I'm 34 and just starting learning this stuff, learned a lot from these guys and learn a ton more everytime I visit these forums. Good luck in your learning and don't ever stop asking questions or looking for answers, hope you stick around.
     
  12. Mar 5, 2017 #11
    They were talking about these giant dark matter stars on How The Universe Works as a candidate for the source of supermassive black holes, any credibility to this?
     
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