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The so-called GZK cosmic rays sometimes have an energy equivalent to a baseball moving at 30 m/s.

The source of these rays has yet to be determined. Could 2 rotating neutron stars orbiting one another use their overlapping magnetic fields to cause atoms in a gas to crash into each other forcefully enough to produce massive cosmic rays, in particular protons and antiprotons. If the gas contained iridium then it is well established in experiments that protons striking iridium atoms can create antiprotons.

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    $\begingroup$ For cosmic rays, you want to accelerate particles faster, not lose energy by colliding them. It could be possible for a neutron star with a very strong magnetic field to generate near the GZK limit, but when I was in the field, AGN were the focal point of research instead (I've been out for about 8 years now, so no clue the state of things now). $\endgroup$
    – Kyle Kanos
    Commented Oct 6, 2023 at 21:48
  • $\begingroup$ Also, could any of the close voters comment on what is unclear here? It looks very straight-forward to me. $\endgroup$
    – Kyle Kanos
    Commented Oct 6, 2023 at 21:49

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A relativistic collision between two particles is generally going to lose energy as some of the energy of the two particles goes into creating secondaries (e.g., the useful $p+p\to p+p+\pi^0$ reaction). So anything starting out with "what if they collide..." ought to fail on that principle alone.

Instead, what you want is something to accelerate a particle from some thermal speed (think Maxwell-Boltzmann) up to the ultra-relativistic speed (e.g., $v\approx c$). There is a class of neutron stars with very strong magnetic fields, called magnetars, that have magnetic fields of $\sim10^{10}$ T, which is quite powerful. From the Lorentz force, $\mathbf{F}\propto\mathbf{v}\times\mathbf{B}$, we can see that a particle can be accelerated due to the magnetic fields; hence this part of your question is quite reasonable: objects with very large magnetic fields can (and probably do) accelerate particles.

The question is then whether the neutron stars (including magnetars) are (dominant?) sources of (near) GZK-limit cosmic rays. To this question, I don't have an answer. When I was researching cosmic rays 8$^+$ years ago, the expectations were that Active Galactic Nuclei were the primary contender for the production of GZK-limit particles. Having taken a non-academic job, I've lost track of where the research is going since then.

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A journal in the issue "Nature" published 1965, indicates Neutron Stars produce cosmic rays. Even as singular units. https://www.nature.com/articles/2061342a0

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  • $\begingroup$ It would be interesting to know how long the hydromagnetic waves can last for in the supernova remnant mentioned in the article. $\endgroup$
    – user379806
    Commented Oct 7, 2023 at 13:18
  • $\begingroup$ The article seems to be discussing galactic cosmic rays rather than extra-galactic cosmic rays, the latter population being those that attain the GZK limits. $\endgroup$
    – Kyle Kanos
    Commented Oct 7, 2023 at 15:25
  • $\begingroup$ @Kyle Kanos One of those extra galactic objects is a blazer called Markarian 421 and a very high energy GZ K was seen coming from its general direction in Ursa Major. There are 2700 blazers known in the universe. Markarian 421 is around 400 million light years away. But there is also a binary star system in Ursa Major. $\endgroup$
    – user379806
    Commented Oct 8, 2023 at 8:52
  • $\begingroup$ @LazyReader The article in Nature mentions waves in the magnetic field accelerating ions. There are 10 million light years magnetic filaments in supercluster s. Perhaps waves in these help to transport GZK ions and prevent cosmic microwave photons from slowing down the GZKs. $\endgroup$
    – user379806
    Commented Oct 8, 2023 at 13:14