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Nutronstars - how they can put out light?

  1. Sep 2, 2013 #1

    Low-Q

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    I have read about nutronstars, that the electrons and the protons merge together forming nutrons. These stars are very small but with a mass density that is unimagineable. Maybe I have missed something in these explanations I have read, but how can matter such as nutrons send out light if there is no free electrons left? Isn't light photons that originaties from electrons that jumps from a high state into a lower state?

    Br.

    Vidar
     
  2. jcsd
  3. Sep 2, 2013 #2
    1) Neutrons can send out light, with some difficulty. Neutrons do not have charge, but they do have magnetic dipole moment, which gives them a feeble ability to emit light.
    2) All charged particles, not only electrons, can freely emit photons. Nuclei contain no electrons, just neutrons and protons, yet they emit gamma rays, which are also photons.
    3) Not all electrons and protons merge together in neutron stars. There are some protons and electrons left even inside neutron star. But light would not get out of neutron star interior anyway. The region near surface of the neutron star, which we can see, still has ordinary protons and electrons, and neutrons in nuclei, so it can freely emit light.
     
  4. Sep 2, 2013 #3

    Vanadium 50

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    Why do you think they put out [much] light?
     
    Last edited: Sep 2, 2013
  5. Sep 2, 2013 #4

    SteamKing

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    1. For one thing, neutron stars can be incredibly hot. The core temperature can be on the order of 100 billion to 1 trillion K for a newly formed neutron star. After a short time, neutrino emission cools the core to about 1 million K, which is still pretty hot. Most of the EM emission at these temps. is in the form of X-rays.

    2. The tremendous gravity of the neutron star is accelerating the surrounding gaseous stellar debris left over from the formation of the star. Once this material is traveling at a good fraction of the speed of light, any collisions within this gas, or by the gas with the surface of the neutron star, will release significant quantities of energy, usually in the form of X-rays.

    3. The highly magnetic and rapidly rotating neutron stars will accelerate charged particles, causing syncrotron emission. This emission can take all forms of EM radiation, including visible light.
     
  6. Sep 2, 2013 #5

    Low-Q

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    Because I assumed the light was put out due to other (to me unknown) mechanisms than electrons changing states. I think the answers given explains it. Thanks to you all.

    Vidar
     
  7. Sep 2, 2013 #6

    Chronos

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    EM emissions are measurably redshifted due to their intense gravity. As already noted, a significant amount of EM can be emitted by infalling matter, which is less heavily redshifted. Neutron stars are very faint at visible light frequencies, and not exactly blindingly bright at x and gamma ray frequencies. In part, this is because of their extremely small surface area compared to 'normal' stars.
     
  8. Sep 2, 2013 #7

    Ken G

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    And let us not forget how neutron stars were first seen-- the radio emissions of pulsars, which involves energy release in a rapidly rotating north-south magnet.
     
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