302K views · 6.3K reactions | The blue glow is called Cherenkov...

The Cherenkov Telescope Array Observatory (CTAO) is the world’s most powerful ground-based gamma-ray observatory. Built in collaboration with European Southern Observatory (ESO), CTAO is designed to detect the most energetic light in the universe: gamma rays. These gamma rays are released during the most violent cosmic events — exploding stars, supernovae, and extreme particle accelerators in space. Gamma rays travel across the universe at the speed of light. When they reach Earth, they collide

We are often taught that nothing can travel faster than the speed of light. This is true in a vacuum (like space). The universal speed limit, c, is unbreakable. But in a material like water, light actually slows down. In water, light travels at about 75% of its vacuum speed. This creates a loophole for high-energy particles. In nuclear reactors, subatomic particles (like electrons) are often ejected at speeds that are incredibly fast—faster than the speed of light *in water* (though still slower