Astrophysicist William Purcell knew that if he looked at the center of the Milky Way, he would see what is known as antimatter: bizarre subatomic particles that resemble ordinary protons and electrons but carry an opposite charge. But when NASA controllers trained the orbiting Compton Gamma Ray Observatory on this core region and beamed the data back, Purcell saw something on his computer screen at Northwestern University that nobody could have predicted: a veritable colossus of antimatter, a vast fountain spewing out from the center of our galaxy and reaching trillions of miles into space.
What could have produced such a...