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Could accretion on a neutron star’s poles cause the jets?

  1. Dec 23, 2015 #1
    Could accreting material on a neutron star’s poles impact with enough energy to initiate fusion reactions, some of which escapes the star as ultra-relativistic jets?
     
  2. jcsd
  3. Dec 23, 2015 #2
    I think on a magnetized neutron star a plateau of accreted material would form and fusion reactions occur there. More than half the EM/light energy from the fusion reactions would exit the star. Half the ionized matter would exit out the magnetic pole and the other half would enter the star and cause more reactions there. Magnetic volcano is not such a good namefor this though it might look like some. Magnetic cannon describes it better. Squirt in a bunch of fuel and it shoots back at you.
     
  4. Dec 23, 2015 #3
    A large amount of plasma fusion reactions might occur far above the plateau. Still its a situation where accreting matter at or near the pole undergoes fusion reactions so a lot of it will shoot back out. If this explains neutron star jets it still doesn't explain why neutron star mass seems to be limited to 2 SM.
     
  5. Dec 23, 2015 #4

    Jonathan Scott

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    It is already assumed that X-ray bursts from neutron stars are caused by material falling onto the surface and immediately undergoing fusion because of the impact energy.
    Jets are not yet fully understood, but quasars also have jets and are thought to involve black holes rather than neutron stars, so the same explanation could not work in that case.
    I've previously heard that jets are probably caused by falling ionised plasma being accelerated out of the equatorial plane towards the polar directions by twisted magnetic fields (from relativistic spinning), but then being partially neutralised (perhaps combining with free electrons or even electrons derived from pair production) so that the resulting neutral material escapes the magnetic field. I'm not up to date with recent research on the subject.
     
  6. Dec 23, 2015 #5
    Sorry to post so much, maybe the above thoughts explain little.

    Do charged particles from fusion reactions even have sufficient energy to escape the surface of a 2 SM neutron star? My guess is no. If so, would whatever escapes a neutron star's surface have to have an ultra-relativistic source? If there is an ultra-relativistic source what choices are there for its location?: (1) above the star surface? (2) at the star surface? (3) on a plateau above the surface? (4) below the surface? (5) the core?

    I think ultra-relativistic conditions could exist at the core. Not so sure about the other places.
     
  7. Dec 23, 2015 #6
    Last I heard some thought that the jets were understood as an effect of general relativity, some disagreed.

    The jets are similar to the jets from black holes, so (1) seems like the frontrunner.
     
  8. Dec 23, 2015 #7
    Sorry, I didn't read your post before posting above.

    "It is already assumed that X-ray bursts from neutron stars are caused by material falling onto the surface and immediately undergoing fusion because of the impact energy."
    Yes, but I wonder if charged particles from fusion reactions even have sufficient energy to escape the surface of a neutron star.

    "Jets are not yet fully understood, but quasars also have jets and are thought to involve black holes rather than neutron stars, so the same explanation could not work in that case."
    True, the above doesn't explain black hole jets. stars. We don't know whats in a black hole. But what happens on a neutron star?

    "I've previously heard that jets are probably caused by falling ionised plasma being accelerated out of the equatorial plane towards the polar directions by twisted magnetic fields (from relativistic spinning), but then being partially neutralised (perhaps combining with free electrons or even electrons derived from pair production) so that the resulting neutral material escapes the magnetic field."
    Why should this ionized plasma become partially neutralized and escape? Does it cool down? Neutral material would not follow magnetic field lines and it looks like the jets closely follow a magnetic pole.
     
  9. Dec 23, 2015 #8
    That makes sense. Gravity, magnetic field, and spin combine above the neutron star's magnetic pole to cause ultra-relativistic conditions to exist. Hmmm.

    Question: Would the ultra-relativistic jet above the neutron star's pole go in both directions, and pierce the surface of the star?
     
  10. Dec 23, 2015 #9
    The crust of a neutron star is very likely the strongest, toughest stuff in the universe. I can't imagine it being pierced by anything. The outer surface is ultradense polymerized iron.
     
  11. Dec 23, 2015 #10
    I think it would depend on the density of the jet but probably an ultra-relativistic jet would cut thru the crust like a hot knife thru butter. Not much can stand up to [tex] \frac{1}{3} \rho c^2[/tex]
     
  12. Dec 24, 2015 #11
    Consider a bubble of ultra-relativistic matter (from the core) propagating along the magnetic field lines that has reached the bottom of the iron crust of the star. Its density should be greater than the density of the iron crust, but even if its density was the same it would cut right thru the crust. The "hardness" effect of the crust shouldn't be able to generate a back pressure nearly equal to (rho)(c^2)/3. I think the gravity on the surface of a neutron star is so strong that the ions directly produced from fusion reactions would have inadequate energy to escape the star! But ultra-relativistic matter would. Ultra-relativistic matter is a different ball game.
     
  13. Dec 24, 2015 #12

    Jonathan Scott

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    This idea of "ultra-relativistic matter" moving around within the core of a neutron star doesn't make sense to me. It's unbelievably dense solid material.
    If it's something you invented, this is not the place to discuss it; this forum is for discussing subjects based on accepted scientific principles.
     
  14. Dec 24, 2015 #13
    Yes, but what are the accepted scientific principles to describe the jets?
     
  15. Dec 24, 2015 #14
    The core of a neutron star is superfluid. The electrons moving about are relativistic. The core is also a proton superconductor.

    Superfluids seem to me to be the same as a superconductor except with neutral particles.

    There was some interest in a quark plasma inner core, but with the discovery of a 1.97 stellar mass neutron star this view has gone out of style.
     
  16. Dec 24, 2015 #15

    Jonathan Scott

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    I stand corrected on the word "solid", thanks. I guess it's a long time since I learned about neutron stars, when I think the core was described as probably being a "lattice" or "crystalline" structure of neutrons, although I think the structure is still somewhat poorly understood even now. I had certainly previously heard that energies were so high that particles would be moving relativistically, but I thought that this was only over tiny distances, and I do not recall having heard of any energy source which could result in a "bubble" or anything else moving at relativistic average speed over macroscopic distances through this material.
     
  17. Dec 24, 2015 #16

    Jonathan Scott

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    As far as I know, the current assumption is that the jets are formed from infalling material which has been deflected towards the poles, possibly by relativistic twisting of magnetic fields. Certainly, strong jets appear to relate to large amounts of infalling material combined with strong magnetic fields. The exact details are not currently understood, but your alternative speculative suggestion that jets might originate on or inside neutron stars does not appear to fit with these current assumptions, and I think that's the best answer we can give to your original question (which however mutated a bit).

    Although it is fun to discuss wildly speculative ideas, this forum is for discussions within the scope of accepted scientific principles, and although I find this frustrating myself, I have seen enough evidence to know the value of these rules. Although a limited amount of scientifically-based speculation may be tolerated, your suggestions seem too vague and speculative to me to be acceptable topics for further discussion. I'm not a mentor, so it's not my job to enforce the rules, but you'll get more help if you try to stay well within the guidelines.
     
  18. Dec 24, 2015 #17
    .

    I'm look for explanations of possible causes of neutron star ultra-relativistic jets and/or what could cause the apparent mass limitation of a neutron star to 2 SM. They don't have to be caused by the same thing.

    Lets consider that outside above the star a magnetic pinch or some other relativistic effect caused a huge concentration of mass-energy. This outside of the star model says this concentration can eject as ultra-relativistic matter. Does the accreting matter never reach the surface of the star but instead blows up above the star or is directed away from the star by fields? Does a magnetic pinch prevent the ultra-relativistic jet from touching the star? This model doesn't explain the apparent mass limitation of 2 SM. To me magnetic jets seem a more sensible way to vent excess mass-energy out of a neutron star. I'd like above the star model of jet formation explained better.
     
  19. Dec 24, 2015 #18
    Forget the original question, we're way past that. Fusion reactions are puny compared to ultra-relativistic matter. Yes, this forum is for discussions within the scope of accepted scientific principles, so I'd like the above the star model of jet formation explained better.
     
  20. Dec 24, 2015 #19

    Jonathan Scott

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    How is your "ultra-relativistic matter" getting its energy?
    I thought the core matter got its additional energy from gravity, in which case lifting it up from the core to the surface will take that energy away again.
     
  21. Dec 24, 2015 #20
    Ultra-relativistic matter travels at a high percentage of c and has enough kinetic energy to escape a neutron star from the core or the surface.

    How can ultra-relativistic matter be formed above a neutron star which has a radius of at least 1.7X the Schwarzschild radius? There isn't enough gravitational energy to make ultra-relativistic matter there. The most energy the accreting matter can get from gravity there is how much ..... maybe 0.3M(c^2) ? Thats less than the energy of some neutron star ultra-relativistic jets.
     
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