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Why do stars emit electromagnetic waves?

  1. Aug 25, 2004 #1
    What process within a star causes it to emit electromagnetic waves (light, x-rays etc.)? What is the source of the electricity / magnetism inside the star?
     
  2. jcsd
  3. Aug 25, 2004 #2
    A Nuclear fusion reaction, that begins with a collision of two hydrogen nuclei (protons) forming a deuterium nucleus, a positron and a neutrino. In the process binding energy (part of the nucleus mass) decreases and is converted into a photon, wich constitutes electromagnetic radiation.
     
  4. Aug 25, 2004 #3
    Thanks for that. Once the electromagnetic radiation "gets started" (so to speak) what determines its intensity, or to put it more crudely, "how far it is able to travel"? In what way, if any, are wavelength, amplitude and frequency determining factors?
     
  5. Aug 25, 2004 #4

    selfAdjoint

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    Wavelength and frequency are of course inversely related; wavelength*frequency = c. The frequency and amplitude are functionally related to the absolute temperature of the source. The functional relationship is called the radiation law. Getting the law right was what led to Planck's discovery of the quantum of action. The temperature at which the peak amplitude occurs is called Wien's law.
     
  6. Aug 25, 2004 #5
    There isn't technically a limit on how far light can travel. However, it gets progressively dimmer when emmited sphereically (as in stars), and can be absorbed by objects in its path.

    Most of these absorptions are of certain frequencies of light. This is why starlight is useful in studying the interstellar media; by the time it reaches us it has been altered in predictable ways by the stuff between. (It was also altered in the begining by the star's atmosphere itself, which provides a great deal of information as well.)
     
  7. Sep 3, 2004 #6
    That is only applicable when involving a stationary source and detector. Maxwell makes that quite clear.
     
  8. Sep 3, 2004 #7

    Tide

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    Most of the electromagnetic radiation in the Sun is generated by dipole radiation (bremsstrahlung) when electrons scatter off of protons. It may take in the order of 100 years for a photon created near the center of the Sun to emerge from the surface based on the very short mean free path of photons in the very dense plasma.
     
  9. Sep 4, 2004 #8

    HallsofIvy

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    Yes, which is why Einstein had to make it clear that it doesn't matter. Everything is stationary relative to something!
     
  10. Sep 14, 2004 #9

    JV

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    It seems to me that you make it more difficult than it is. I think that the majority of the EM-radiator of the sun is created by the fact that the surface of the sun is very hot. And like everything that is hot, it produces photons. I mean even your radiator produces infrared. Right? Or did I miss the point?
     
  11. Sep 14, 2004 #10

    Tide

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    The question was what is the process. Just saying it's hot doesn't get you there.
     
  12. Sep 14, 2004 #11

    selfAdjoint

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    Heat is atoms jiggling. Atoms have electrons and protons. Electrons and Protons have electric charges. Jiggling involves acceleration. Maxwell's laws of electromagnetism require that accelerated charges radiate EM. QED.
     
  13. Sep 14, 2004 #12
    Nothing is ever stationary. All objects are in constant motion. It was noticed that when applying Maxwell's equations to moving objects, that they did not uphold his conclusions. To correct this fallacy, Lorentz introduced the Lorentz Transform, which I have yet to see how that can take in account of lag. What do I know though? Nothing! :rofl:
     
  14. Sep 15, 2004 #13

    Nereid

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    I'm not sure what you're trying to point out here ... if you observe light (EM in general) from a distant source and measure the light's wavelength, frequency, and speed, you will find that "wavelength*frequency = c", as SelfAdjoint said. If you talk with your friend, in a distant galaxy which you perceive is receding from you at close to c, and ask what she measured (for the 'same light' that you detected), she will tell you that "wavelength*frequency = c", where "c" is the same as the value you obtained. Of course, her values for wavelength and frequency will be quite different from the ones you obtained with your detectors.

    Can you clarify please? What is it which 'Maxwell makes [...] quite clear'?
     
  15. Sep 15, 2004 #14

    Chronos

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    Two cents: Gravity is the real culprit [gravity gets blamed for just about everything in the universe]. Gravity is what causes the star to form in the first place and gravity is what powers the fusion process responsible for EM emissions. So you could say that stellar emissions are gravity converted to EM.
     
  16. Sep 22, 2004 #15

    Tom Mattson

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    Without specifying a reference frame, that statement is meaningless. All massive objects are stationary with respect to some origin.

    Ditto for this statement. It is true that everything is in motion with respect to some origin, but without that qualification the statement is meaningless.

    The Lorentz transforms upholds the experimentally verified fact that the laws of electrodynamics are the same for observers in different inertial frames. The LT does exactly what it is supposed to do.
     
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