The Echoes of Light

Twenty years ago, Andrea Tiengo was a junior scientist watching data stream in from a distant space telescope. He was keeping tabs on routine waves of cosmic X-rays washing over the orbiting, bus-size contraption, relayed to his computer on Earth. 

One December afternoon, a peculiar X-ray signal came in. “I saw something like fog, or something blurry, around the point source,” Tiengo says. This one looked different, but it looked so different from any other X-ray observation he had seen that he thought it could be a problem with the hardware. It was getting late in the day, and Tiengo decided to go home and wait to address the problem in the morning. That, he says, “was a big mistake.” 

By the next day, the glow was no longer visible to the telescope—and other researchers, instead of him, had made . That fog-like signal was the first rings of X-ray “light” from a brilliant gamma-ray