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.

Observations from NASA's Chandra X-ray Observatory, Europe's XMM-Newton, and other telescopes have for instance revealed magnetic fields threading the relics that are far stronger than our models predicted. The shock waves of these relics also appear to have strengths that differ depending on whether they're measured in radio or X-ray light.

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