At the universe's grandest scales, galaxy clusters collide in slow-motion cataclysms, leaving behind immense, ghostly arcs — vast ribbons of diffuse radio emissions that can stretch across millions of light-years. Forged by gigantic shock waves that accelerate electrons to near-light speed, these strange structures are known as "radio relics."
Astronomers have cataloged dozens of them, yet their behavior has remained remarkably difficult to explain.
