Dark lightning is a burst of gamma rays that is produced by the collision of extremely fast moving electrons and air molecules that takes place during thunderstorms. Researchers also refer to it as a terrestrial gamma ray flash. Different from regular lightning, dark lightning is a release of high-energy gamma radiation—sources include supernovae and supermassive black holes—that is completely invisible to the human eye. Attempts to understand this mystery haven't turned out so well, because, like normal lightning, the bolts are fleeting.