Scientists complete array on Mexican volcano

An international team of astrophysicists has completed an advanced detector to map the most energetic phenomena in the universe. On Thursday, atop Volcán Sierra Negra, on a flat ledge near the highest point in Mexico, technicians filled the last of a collection of 300 cylindrical vats containing millions of gallons of ultrapure water. Together, the vats serve as the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, a vast particle detector covering an area larger than 5 acres. Scienti...