If my understanding is correct, black body radiation is emitted by a substance due to the substances coupling with the electric field. The negatively charged electrons in atoms for example can couple with the electromagnetic field to turn thermal vibrational energy into black body radiation, hence ordinary baryonic matter can radiate black body radiation. A neutron, however, has no such charge, so it cannot couple to the electromagnetic field in this way. A neutron does have a magnetic moment which might be able to allow for some interaction with an EM field but perhaps not in the same way. Regardless, I want to know how a neutron star (an object that I will assume for the sake of the question to be made purely of neutrons) can emit black body radiation? If it does, does its spectrum resemble that of a normal blackbody?

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    $\begingroup$ Maybe the question needs some clarification. An atom can be electrically neutral overall, but a substances made of neutral atoms can still radiate like a blackbody. Similarly, a neutron is electrically neutral overall, but it's made of electrically-charged constituents (quarks), just like an atom is made of electrically-charged constituents, and the same is true for a neutron star. Are you asking if blackbody radiation depends on the scale at which the charged constituents are bound, or something like that? $\endgroup$ Dec 9, 2020 at 1:59
  • $\begingroup$ Neutron stars have a charged components (mostly protons and electrons). For pure neutron matter, it is possible to consider non-minimal coupling of the neutron with the electromagnetic field (minimal coupling is via the monopole: the electric charge) Role of the vacuum energy in the thermodynamics of neutron matter. I think that the most interesting point is "if blackbody radiation depends on the scale at which the charged constituents are bound" (see @ChiralAnomaly comment). Related: physics.stackexchange.com/q/793441/226902 $\endgroup$
    – Quillo
    Dec 14, 2023 at 6:23

1 Answer 1


from wiki:

Current models indicate that matter at the surface of a neutron star is composed of ordinary atomic nuclei crushed into a solid lattice with a sea of electrons flowing through the gaps between them. It is possible that the nuclei at the surface are iron, due to iron's high binding energy per nucleon.[45] It is also possible that heavy elements, such as iron, simply sink beneath the surface, leaving only light nuclei like helium and hydrogen

Therefore, contrary to your assumption, the surface of the neutron star isnt entirely made of neutron, explaining the (weak) blackbody radiation


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