The most powerful explosions in the modern-day universe, they most likely are caused by the explosion of a supergiant star and the accompanying collapse of its core to form a black hole. The explosion’s gamma rays are funneled into narrow beams from the star’s poles. From Earth, we see a gamma-ray burst only when such a beam sweeps across our planet. A typical gamma-ray burst produces more energy in a few hours than the Sun will produce in its entire lifetime.