What causes Cerenkov radiation?

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I read that Cerenkov radiation is caused by charged particles traveling faster than the speed of light in the medium, but I don't understand why. I have seen analogies to a plane moving a supersonic speed creating a cone of sound waves because the waves can't keep up with the plane, but in this case the sound waves already exist even without the plane traveling faster than the speed of sound. Charged particles don't emit radiation traveling at constant speeds unless traveling faster than the speed of light, so why do they do this if they don't emit any light to begin with when traveling at slower speeds? Does a build up of electromagnetic disturbances somehow create the photons?
 

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e.bar.goum
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I read that Cerenkov radiation is caused by charged particles traveling faster than the speed of light in the medium, but I don't understand why. I have seen analogies to a plane moving a supersonic speed creating a cone of sound waves because the waves can't keep up with the plane, but in this case the sound waves already exist even without the plane traveling faster than the speed of sound. Charged particles don't emit radiation traveling at constant speeds unless traveling faster than the speed of light, so why do they do this if they don't emit any light to begin with when traveling at slower speeds? Does a build up of electromagnetic disturbances somehow create the photons?
From the wiki page for Cherenkov radiation: https://en.wikipedia.org/wiki/Cherenkov_radiation

As a charged particle travels, it disrupts the local electromagnetic field in its medium. In particular, the medium becomes electrically polarized by the particle's electric field. If the particle travels slowly then the disturbance elastically relaxes back to mechanical equilibrium as the particle passes. When the particle is traveling fast enough, however, the limited response speed of the medium means that a disturbance is left in the wake of the particle, and the energy contained in this disturbance radiates as a coherent shockwave.
 
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Simon Bridge
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As a charged particle travels, it disrupts the local electromagnetic field in its medium. In particular, the medium becomes electrically polarized by the particle's electric field. If the particle travels slowly then the disturbance elastically relaxes back to mechanical equilibrium as the particle passes. When the particle is traveling fast enough, however, the limited response speed of the medium means that a disturbance is left in the wake of the particle, and the energy contained in this disturbance radiates as a coherent shockwave.
https://en.wikipedia.org/wiki/Cherenkov_radiation

Also:
https://www.physicsforums.com/threads/what-causes-cherenkov-radiation.595888/
http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/cherenkov.html

[edit] beaten to it!
 
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