What hold the electrons in orbit? Is it gravity or the atomic attraction between the protons and neutrons?

I asked this question on Physics SE I hope I improved on the quality enough to do better here.

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Is the light we see from a neutron star from the neutrons or the electrons?

  • $\begingroup$ Have you read curious.astro.cornell.edu/physics/80-the-universe/… $\endgroup$
    – James K
    Feb 7, 2018 at 6:56
  • $\begingroup$ @JamesK that article is a very poor answer to the question that is its title, and contains factual errors/gross simplifications. $\endgroup$
    – ProfRob
    Feb 7, 2018 at 9:48
  • 3
    $\begingroup$ I asked this question on Physics SE Cross posting is, at best, discouraged. Please provide a link to that question. And the images in your question are not useful - in general it is preferred that people did not just add arbitrary images that don't provide information relevant to the question. They're just distracting from the question itself. $\endgroup$ Feb 7, 2018 at 11:29

1 Answer 1


The visible "surface" of the neutron star contains no free neutrons. It consists of completely ionised atomic nuclei and free electrons. The exact composition is uncertain - either at or just below the surface will consist of iron-peak elements, becoming increasingly neutron-rich with depth, however the outer few cm (which is where any electromagnetic radiation arises) could consist of ionised hydrogen and helium that has been accreted.

Neutron stars also have magnetospheres and these are also a source of radiation. Charged particles are accelerated away from the neutron star magnetic poles, spiral in the magnetic fields and emit (mainly the electrons, which undergo more extreme acceleration) synchrotron and curvature radiation.

The high density "neutron fluid", containing mostly free neutrons, with a small proportion of protons and electrons, is not reached until about 1-2 km below the neutron star surface.


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