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The colour of a neutron star?

  1. Sep 21, 2012 #1
    I was wondering today what is the colour of pure neutrons confined together, I'd guess it's either completely black or white, because it doesn't have the electric orbitals needed to generate different wavelengths. I'm generally guessing it just reflects light and is therefore what.... maybe a mirror?

    And I am mainly meaning the matter neutrons confined, and disregarding that electrons may be flowing at the outermost layer of a neutron star.

    So what is the colour of pure pressurized neutrons, but what about the neutrons star like it is inclunding the electrons flowing around and such?

    Are there any studies done on this?
  2. jcsd
  3. Sep 21, 2012 #2
    If they were simple neutrons it might be clear like glass. But in fact they are a seething complex of charged and uncharged states.

    My guess is they would have something of a dark metallic shiny sheen like polished hematite. Just a guess though.
  4. Sep 21, 2012 #3
  5. Sep 21, 2012 #4
  6. Sep 22, 2012 #5

    Neutrons have no charge, so neutrons confined together would be transparent.

    Neutron star cores have a few percent of electrons and protons which scatter light. I think it would be translucent like an extremely dense fog. The spectrum of the radiation would depend on the temperature of the star, which varies greatly. It is quite complicated and depends on many things, so I have no idea what temperature a very old neutron star would have. But there is so much energy kicking around in a neutron star that I think it is safe to assume that everything in the star is glowing intensely for the next quadrillion years.
  7. Sep 22, 2012 #6

    Vanadium 50

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    Neutron stars are at millions to tens of thousands of degrees, so they would appear blue-white. Until your eyeballs melt.
  8. Sep 22, 2012 #7
    Jarfi: I don't understand what question you are asking, but I'd reply in a general way as did Vanadium....
    stars are really, really, hot...so most of the 'color' you see reflects that heat.

    You can see a photo of a neutron stars here and draw your own conclusions:

    'Confinement' may have a variety of meanings....neutrons, for example, may be 'confined' in nuclei.

    I suspect that the color of any particle compressed or confined to the densities of a neutron star would reflect primarily super hot temperatures....how that relates to the particles themselves is a different issue. For example, do fusion and fission reactions have significantly different colors?? How does that reflect the particles involved?
  9. Sep 22, 2012 #8
    What does this mean?? How is electromagnetic charge related to transparency or color??

    In general charge is reflected as an additional component of total energy...a component other than beyond mc2
    Last edited: Sep 22, 2012
  10. Sep 22, 2012 #9

    Okok I've read all those posts but let me adress "Neutrons have no charge, so neutrons confined together would be transparent." specifically.

    You say neutrons have no charge? well so do hydrogen atoms but the INNER STRUCTURE has charge, the atom is made from a - and a + charge... and the neutron is made fro 2/3 - and + charges, so according to that... an neutron HAS charges confined within it, but the whole sum of charges is zero exactly like atoms.

    In order for light to be created, a charge must move, but I am very curious on how this scenario works for a single neutron, I suspect the picture taken of neutron stars with light to be originated from electron clouds surrounding the neutron star.

    I am hypothetically now thinking about the neutron star matter neutrons. Without any electrons fizzing around.

    Now some say transparent, but if a photon were to hit a neutron, it would hit one of the charged quarks and refract, reflect or be absorbed. It's like people are saying different answers, but is there no one academically accepted outcome of this?

    and at last, I think in the end it depends on how you look at a neutron, I don't know if this has been looked at but it's also what I have been pondering... maybe the way a neutron affects a photon, depends on if the neutron IS three quarks stuck together by gluons, but if you smash them they scatter into other things..... OR the neutron IS simply a neutron, and doesn't have an inner structure UNTIL you smash it so it becomes an unstable particle at that energy level and dechays into quarks and photons etc.

    I don't know if this is answerable, or if you understand what I mean, but generally i mean, is the neutron a single entity until at high energies it is unstable as one and changes into quarks and more with the sum of it's energy same as the original neutron, or was the neutrons three quarks that always were there and just god loose at this temperature.

    also... the notion that quarks can't exist alone must have something to do with this?

    I think... that maybe the experiment of looking at how the what can I call it, grey matter in a neutron star affects light, can show us what a neutron really is, not just philosophically.

    anybody have any take on this?
  11. Sep 22, 2012 #10
    Don't neutron stars consist of a sea of degenerate electrons and angular momentum ?
    Would that have any bearing to their EM spectrum.
  12. Sep 22, 2012 #11
    Neutron stars can be thought of as protons and electrons squished into a single entity...neutrons. Theelectron degeneracy pressure has been overcome.
  13. Sep 22, 2012 #12
    Oh yes, that makes sense. I was getting mixed up between neutron stars and white dwarfs since they both are stabilized by degeneracy pressure.

    Does this mean the star on the whole is neutral ,as someone else before me suggested (above) but how can it be like that when we know neutron stars have strong magnetic field with some going up to 1 trillion Gauss , unless there still is a fraction of electrons on the surface giving rise to the B-field ?

    P.S: Sorry if my questions sounds silly...
  14. Sep 22, 2012 #13


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    Neutron stars are pretty much electrically neutral. The magnetic fields arise from a magnetohydrodynamic dynamo process.

    From wikipedia's article on Magnetars: http://en.wikipedia.org/wiki/Magnetar

  15. Sep 22, 2012 #14


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  17. Sep 22, 2012 #16


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  18. Sep 22, 2012 #17
    Air is transparent to light but is full of charged particles. I don't understand it, but apparently the charges in the molecules cancel so that light passes through. It depends on the particular molecule and the wavelength of the light.

    My guess is that neutrons might absorb very high frequency EM with very short wave lengths but certainly not visible light.

    The free protons and electrons buzzing around in the neutron star core scatter the light.

    Neutron star core physics is very exotic and intuition is not of much use there, but this is the best I can do.

    A quark plasma IS possible and has been created at CERN. Such a thing might form in the center of a neutron star but the consensus these days is no, because the star is too cold and the pressure not quite high enough. It is quite possible that there are stable exotic particles in the center, but we do not know how much pressure there is there.
  19. Sep 22, 2012 #18
    Most neutron stars are not magnetars and never have such a dynamo. Even in the magnetars the dynamo exists for only a very short time in the very early life of the star.

    Neutron stars inherit part of the magnetic field of the parent star. They also generate an internal magnetic field by rotation of protons and electrons but very little is known about that.
  20. Sep 22, 2012 #19
    Not entirely. In neutron star cores there are about 2% electrons and protons and possibly other exotic particles. This gradually blends into a crust of heavy metals and a sea and/or atmosphere of carbon. There is often a layer of hydrogen/helium from space that periodically explodes thermonuclearly.
  21. Sep 22, 2012 #20

    Neutron stars are so small that they are very difficult to see. Usually what is visible is the hot gas in the neighborhood. I did read of one case of a neutron star that was directly visible. It was unusually close to Earth and had no gas around it. I think it would be quite faint.
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