US satellites hunting nuclear tests accidentally found first gamma-ray burst

For more than half a century, gamma-ray bursts have remained one of the most puzzling events observed in space. These bursts are sudden flashes of gamma rays, a very high-energy form of light. They can appear from almost any direction in the sky and can last from less than a second to several minutes.The discovery of the gamma rays happened very unexpectedly. According to NASA, in July 1967, US satellites called Vela 3 and Vela 4 were watching for signs of nuclear weapons tests that could violate the Nuclear Test Ban Treaty. Instead, the satellites detected brief flashes of high-energy photons or gamma rays coming from space.At first, scientists did not know what they were seeing. Some thought the bursts might be coming from somewhere relatively close to Earth, perhaps within the Solar System or the Milky Way. Others believed they could be coming from much farther away.