They’re the most impressive explosions the universe has been able to offer after the tremendous effort of the Big Bang. If one happened anywhere near Earth (and by near I mean within a thousand light years or so, so ‘near’ only a cosmic scale) and and was pointed at us, the radiation would kill all life here. Even the cockroaches (probably).
Up until now, prevailing thought had it that they were formed by the collapse into a black hole of a supermassive star. Now, however, a new theory is being considered (again): that they occur as the result of a black hole burrowing into the middle of a star and then consuming it. A sort of cosmic Alien, if you will.
Happily for us they’re directional, and it seems that they’re more likely to happen on the outer edges of the universe. Scientists have posited that this is because that’s where the older stars are, and the differences in chemistry between older stars and newer stars means newer ones are more likely to be prosaic about the matter and avoid the huge effort involved in producing a gamma-ray burst. Maybe. Another theory says they occur in regions with low metallicity (not a feature of the Milky Way, happily).
Either way, they’re fascinating beasts and something to keep an eye on (possibly one wearing sunglasses). For those of you interested, we apparently pick up about one a day…