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Does a neutron star act like a big particle?

  1. Feb 16, 2015 #1
    The fastest moving pulsars are theoretically spinning neutron stars. They probably got their velocity from a kick from a supernova like Project Orion.
    http://chandra.harvard.edu/photo/2012/igrj11014/
    http://chandra.harvard.edu/photo/2003/b1957/closer_look.html
    As I understand it, neutron stars have collapsed down to just the elementary particles of atoms. The question is, would such a star act like a particle and interact with photons like electrons and other free particles? I am intrigued with the fact that photons when hit by free particles convert to electrons and positrons. When an electron was simultaneously hit by 4 photons whose energy added up to the E=mC^2 energy of two electron masses they created an electron positron pair.
    http://www.hep.princeton.edu/~mcdonald/e144/science1202.html
    If the neutron star acts like a big particle it should have a huge cross-section many orders of magnitude larger than an electron and then could simultaneously interact with many orders of magnitude more less energetic photons to create electrons and positrons?
     
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  3. Feb 16, 2015 #2

    DaveC426913

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    A neutron star is not a simple, naked object. It generally has a neutronium core, surrounded by a layer of highly-compressed regular matter.
    That probably muddles the concept of it acting to outward appearances like a large particle.

    500px-Neutron_star_cross_section.svg.png
     
  4. Feb 16, 2015 #3
    The elementary particles of atoms are the quarks and electrons. A neutron star is a massive clump of neutrons that formed from a stellar collapse. therefore there are no electrons which are a necessary component of atoms, otherwise it's just nucleons. And there can't be any protons.
     
  5. Feb 16, 2015 #4

    SteamKing

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    Actually, the spin of a neutron star is provided by the conservation of angular momentum from the original core of the star, which went supernova to form the neutron star. In order for this angular momentum to remain constant, the neutron star, which is much smaller than the original stellar core, must increase its rotational velocity by several orders of magnitude.

    The composition of a neutron star is a bit more complex than you apparently have been led to believe. Sure there are a lot of neutrons in a neutron star, but there is a complex mixture of leftover atomic material from the original star (mostly iron) at the surface, and a lot of exotic particles deeper inside the neutron star. The exact composition is still not completely understood.

    http://en.wikipedia.org/wiki/Neutron_star

    There are many interactions between a neutron star and its surroundings. The magnetic field around such an object is quite strong, and this field can accelerate particles to very high speeds. It is through some of these interactions that we can observe neutron stars, sometimes optically, but more commonly by other portions of the EM spectrum.
     
  6. Feb 18, 2015 #5
    I am particularly interested in how neutron star interacts with photons (on a microscopic scale). If the neutron star acted like a big particle, its mass would produce almost no Compton effect red shift since the Compton effect red shift is inversely proportional to the mass of the particle. But what would electron-positron production be like? I'm not sure what the probability of such interactions are wrt the mass of the particle. Since there are basically no atoms in the neutron star, it would seem unlikely that photons would be absorbed by raising electrons to higher energy levels in atoms or causing ionization.
     
  7. Feb 18, 2015 #6

    DaveC426913

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    Did you look at the diagram above? Most of a neutron star is electrons, neutrons and nuclei.
     
  8. Feb 18, 2015 #7
    But they are squeezed together very tightly. What happens to a photon whose wavelength is larger than the size of a cluster of several such particle items when it hits them? Does it change into positrons and electrons or just get reflected? How is energy and momentum conserved? The neutron star is not a black hole. At least one of the pulsars, B1957+20, is travelling at higher than escape velocity from the galaxy, heading into intergalactic space. I am wondering if such a runaway object could also be absorbing photons in a runaway fashion without being a black hole. If it is increasing in particle and antiparticle mass, could it eventually become the center of a new galaxy in intergalactic space?
     
  9. Feb 18, 2015 #8

    SteamKing

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    Or it could just be another neutron star wandering the vast void between galaxies.

    Although it's not clear exactly how much matter occupies the space between galaxies, there is everything from isolated stars up to clusters like the Magellanic Clouds swirling around out there. It's pretty slim pickings from which to pick up enough material to start a new galaxy.
     
  10. Feb 18, 2015 #9
    But if it's moving rapidly through the cosmic background radiation and also being hit by gamma rays and x-rays from all sides and if it could convert this energy to electrons and positrons (as happened in the SLAC experiment linked to in my initial question), then the pickings might not be so slim.
     
  11. Feb 18, 2015 #10

    SteamKing

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    Trust me, the amount of matter contained in even a small star would require a lot of photons to be converted into not only electron-positron pairs, but much heavier particles, like protons. For the most part, electron-positron pairs don't tend to stick around long: they usually wind up annihilating one another, producing a couple of gamma rays.
     
  12. Feb 18, 2015 #11
  13. Feb 20, 2015 #12
    NASA has had a program to look at advanced propulsion systems. One of these is matter-anti-matter propellant. I would think that electrons and positrons being created in pulsars would be trapped in their magnetic field. At the poles of the magnetic fields where the field lines come together would seem to be where the trapped particles would be more likely to collide and annihilate. This could provide a radiation pressure force being applied to the neutron star and giving it its velocity in a preferred direction. LGM doing intergalactic travel. The neutron star makes a good radiation shield. Sounds a lot like a bigger scale Project Orion. There might be a sci-fi book here. lol.
     
  14. Feb 20, 2015 #13

    DaveC426913

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    Sure, in the same way a jumper made of plutonium would make a good radiation suit...
     
  15. Feb 20, 2015 #14
    The LGM are down inside the neutron star shelter, away from the emitters of x-rays and gamma rays. lol.
     
  16. Feb 21, 2015 #15
    The annihilation of a positron and electron results in the emission of just a single gamma ray. In the forward direction of the fast moving pulsar, the incoming gamma rays are blue shifted into the wavelength where they have enough energy to become electrons and positrons when they collide with the pulsar trapped electrons head-on. Then they spiral along the pulsar magnetic field where they annihilate on the rearward pole to provide the pulsar propulsion exhaust blast like Project Orion. This almost seems to be a violation of thermodynamics' second law.
     
  17. Feb 21, 2015 #16

    Nugatory

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    It would be a good exercise to calculate just how much blue shift we're talking about here.
    You should also consider that the incoming radiation transfers momentum to the moving object in the interaction that leads to the pair production.
    And finally, you should ask yourself where the energy released in the annihilation was before annihilation.

    This thread is closed.
     
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