These ultrabright flashes have recently been tracked for days, upending ideas about the cataclysms that create them. The Cherenkov Telescope Array, currently under construction, will use a network of more than 100 ground-based telescopes such as this one to monitor the long afterglows of ultrahigh-energy gamma-ray bursts.In July 1967, at the height of the Cold War, American satellites that had been launched to look for Soviet nuclear weapons tests found something wholly unexpected. The Vela 3 and 4 satellites observed brief flashes of high-energy photons, or gamma rays, that appeared to be coming from space. Later, in a 1973...