In the summer of 2010, Oxford University physicist Justin Wark flew to Northern California to study the interiors of stars. The instrument he sought there was not a telescope, but rather a new kind of laser, more than 3,500 feet long and capable of emitting X-rays a billion times brighter than anything ever generated on Earth. It was worth the airfare. In the 60 hours he spent bombarding metal foils with X-rays — creating analogs to stellar plasma, or ionized gas — Wark pulled more data than he had from any single experiment in a quarter century.