Cherenkov [Cerenkov] radiation (P.A. Cherenkov)
Radiation emitted through a massive particle that is moving faster than light in the medium by which it is travelling. None of particle can travel faster than light in vacuum, however the speed of light in other media, like water, glass, etc., are significantly lower. Cherenkov radiation is the electromagnetic analogue of the sonic boom, by Cherenkov radiation is a shockwave set up into the electromagnetic field.