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It seems that in common ways how to produce light (electromagnetic waves, photons) must be involved particles with electric charge: accelerating electrons, spontaneous or stimulated emission, gamma rays from (charged) nuclei. Is it possible to create a photon without electric charge?

Two or three ways came to my mind:

  1. annihilation of neutron and antineutron which would produce two photons
  2. Hawking radiation of black holes (virtual pair of photons is created in vacuum just above the horizon and one of them is captured by the black hole)
  3. rare mode of free neutron decay to proton, electron and electron antineutrino plus gamma ray, but in this case - according to Wikipedia - "gamma ray may be thought of as a sort of "internal bremsstrahlung" that arises as the emitted beta particle interacts with the charge of the proton in an electromagnetic way".
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Another example - neutron acceleration (say, in gravitational field), as neutrons have magnetic moment.

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  • $\begingroup$ So magnetic moment is enough to create photons? $\endgroup$ – Leos Ondra Dec 6 '16 at 13:20
  • $\begingroup$ @LeosOndra: Yes. en.wikipedia.org/wiki/… $\endgroup$ – akhmeteli Dec 6 '16 at 14:57
  • $\begingroup$ Why I'm not surprised? Since the neutron can be accelerated by photons and by this some momentum over goes to the neutron so during deceleration some photons have to be realized. $\endgroup$ – HolgerFiedler Dec 6 '16 at 15:49
  • $\begingroup$ @HolgerFiedler: But I mentioned acceleration by gravitation field, not by photons. $\endgroup$ – akhmeteli Dec 6 '16 at 17:49
  • $\begingroup$ Reading the Wikipedia article on Neutron magnetic moment (en.wikipedia.org/wiki/Neutron_magnetic_moment) I think that its magnetic moment arises from charged quarks inside, so we are again at electric charge, isn't it? $\endgroup$ – Leos Ondra Dec 6 '16 at 18:00
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There's something (not confirmed) called the Hawking-Unruh Effect. It's similar to Hawking radiation, but instead of a black hole, this effect involves an accelerating observer.

It's a strange sort of thing, since an observer at rest wouldn't see the black-body radiation, but the accelerating observer would.

One note: Neutrons only have a magnetic field because they are made of electrically charged quarks. Fundamental particles with no electric charge also have no magnetic dipole.

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  • $\begingroup$ So far it seems to me that Hawking or Unruh radiation are the only candidates for photon creation without electric charge.... But are they radiation of photons or particles? $\endgroup$ – Leos Ondra Dec 6 '16 at 18:04
  • $\begingroup$ @DavidElm Your final note is not quite correct. For example, the Standard Model neutrino spends part of its time as an electron-$W$ loop, from which it acquires a small magnetic moment. $\endgroup$ – rob Dec 7 '16 at 3:12
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    $\begingroup$ It looks like it's possible that neutrinos have a magnetic moment, but this doesn't seemed to have been verified. en.wikipedia.org/wiki/Neutrino#Properties_and_reactions $\endgroup$ – David Elm Dec 7 '16 at 7:46
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Neutrino and antineutrino annihilation results in 3 photons

Neutrino and antineutrino creates Z boson which decays to 3 photons.

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    $\begingroup$ Do you have a reference for that reaction? $\endgroup$ – PM 2Ring May 6 at 23:28
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    $\begingroup$ @PM2Ring It seems like a valid channel, however the cross section would be astronomically small. $\endgroup$ – mmeent May 7 at 17:16

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