Physics & Math / Telescopes

The Mystery of the Rocketing Particles That Shouldn't Exist

From deep space, cosmic rays come fast and pack a heck of a punch. They may also carry clues to the most vexing mysteries in the universe. 

The Advanced Thin Ionization Calorimeter, shown here in Antarctica
before a 2005 launch, detected cosmic rays in the upper atmosphere.

Image Courtesy of T, Gregory Guzik, ATIC

Nothing on the tree-less plains of western Argentina seems to expend much energy. Cattle stand nearly motionless as they graze on the thin grass, which grows slowly in the dry heat and high altitude. A cylindrical water tank with a small solar panel and a skyward-facing antenna sits unobtrusively in the nearly motionless landscape. But hidden within this scene is plenty of drama. At any given moment, millions of projectiles from deep space are raining down, penetrating every object in their path. Each particle then vanishes without a trace—unless it happens to pass through the water tank, where it causes a mi­nute spark visible to scientists thousands of miles away.

The tank is one of 1,600 spaced out at one-mile intervals over 1,100 square miles of land, an area bigger than Rhode Island. Collectively they make up the Pierre Auger Cosmic Ray Observatory, a $50 million physics experiment to study bits of atomic shrapnel that blast out from some of the most violent places in the universe. These energetic particles, called (somewhat misleadingly) cosmic rays, tell revealing tales about the exploding stars and black holes that have shaped galaxies and seeded the cosmos with the essential elements of life...