Cerenkov light

Cerenkov light is the blue glow produced when a charged particle, like an electron, travels through a medium such as water or glass faster than light can move through that same material. Although nothing can surpass the speed of light in a vacuum, particles can exceed the light speed in different materials. This rapid movement disturbs the electromagnetic field, releasing energy as visible radiation — Cerenkov light. It's similar to a sonic boom but with light, creating a characteristic blue glow used in scientific detectors to identify high-energy particles.