By Ron Cowen
Not long ago, physicists seeking to understand the cataclysmic events at the birth of the universe had to rely on massive, earthbound experiments in which beams of charged particles, steered by powerful magnetic fields, traveled in circles for miles before smashing into each other. Now, an increasing number of these particle physicists have turned to the skies, teaming with astronomers to launch spacecraft that can capture gamma rays from astrophysical processes with energies far greater than anything that can be generated in the most powerful atom smashers on Earth.
Carrying thousands to billions of times as much energy as visible-light photons, gamma rays “are telling us about the most energetic processes in the universe,” says David Thompson of NASA’s Goddard Space Flight Center in Greenbelt, Md. But detecting gamma radiation is no easy feat. Scientists have built a variety of ground-based detectors that capture the secondary radiation created when gamma rays crash into gas molecules in Earth’s atmosphere, but only a detector above the atmosphere can capture gamma rays directly.