One of the main reasons this was so bright was that relative to the thousands of other gamma ray bursts astronomers have seen, the monster was pretty close, even at 3.7 billion light-years. A light-year is almost 6 trillion miles.
Most of the bursts NASA telescopes have seen have been twice as distant as this one. Other explosions could be this big, but are so much farther away, they don't seem so bright when they get to Earth, the studies' authors say.
Astronomers say it's incredibly unlikely that a gamma ray burst -- especially a big one like this -- could go off in our galaxy, near us. Harvard's Avi Loeb, who wasn't part of the studies, put the odds at at least 1 in 10 million.
Also, a burst has to be pointing at you to be seen and to be dangerous. It's concentrated like a focused searchlight or death beam. Planets caught in one would lose their atmospheres instantly and would be left a burnt cinder, astronomers say.
"Either it's pointed at us or it's not," Preece said. "If it's not, yay! Civilization survives and we see maybe a supernova. If it were pointed at us, then it matters very much how far away it is in our galaxy. If it's in our local arm, well, we had a good run."
We don't see gamma ray bursts on the surface of Earth because the atmosphere obscures them and because their light is the type we cannot see with our eyes, but NASA has satellites that look for them.
For scientists who look for gamma ray bursts, this was a wow moment.
"These are really neat explosions," said Peter Michelson, a Stanford physicist who is the chief scientist for one of the instruments on a NASA gamma ray burst-spotting telescope. "If you like fireworks, you can't beat these. Other than the Big Bang itself, these are the biggest there are."
The burst "is part of the cycle of birth and life and death in the universe," Michelson said. "You and I are made of the stuff that came from a supernova."