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:
- anihilation of neutron and anineutron which would produce two photons
- 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)
- 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".