WASHINGTON -- Astronomers call it the monster. It was the biggest and brightest cosmic explosion ever witnessed. Had it been closer, Earth would have been toast.
Because the blast was 3.7 billion light-years away, mankind was spared. But orbiting telescopes got the fireworks show of a lifetime in April.
The only bigger display astronomers know of was the Big Bang that created the universe, and no one was around to see that.
What happened was a gamma ray burst, an explosion that happens when a massive star dies, collapses into a brand-new black hole, creates a supernova and ejects energetic radiation that is as bright as can be as it travels across the universe at the speed of light.
NASA telescopes in orbit have been seeing these types of bursts for more than two decades, spotting one every couple of days. But this one was special. It set records, according to four studies published Thursday in the journal Science.
It flooded NASA instruments with five times the energy of its nearest competitor, a blast in 1999, said University of Alabama at Huntsville astrophysicist Rob Preece, author of one of the studies.
It started with a star that has 20 to 30 times the mass of our sun, but is only a couple of times bigger, so it's incredibly dense. It exploded in a certain violent way.
In general, gamma ray bursts are "the most titanic explosions in the universe," Mr. Preece said, and the one witnessed last spring was so big that some of the telescope instruments hit their peak. It was far stronger and lasted longer than previous ones.
"I call it the monster," Mr. Preece said. And he wasn't alone. One of the other studies, not written by Mr. Preece, used the word "monster" in its title, unusual language for a scientific report.
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. Other explosions could be this big, but they're so much farther away that 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 one as big as this -- could go off in our galaxy, near us. Harvard University'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 be left as a burnt cinder, astronomers say.
People don't see gamma ray bursts from the Earth's surface because the atmosphere obscures them and because their light is of a type we can't see with our eyes. But NASA has satellites that look for them. And for scientists who look for gamma ray bursts, this was a wow moment.
"These are really neat explosions," said Stanford physicist Peter Michelson, chief scientist for one of the instruments on a NASA gamma ray burst-spotting telescope. "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," Mr. Michelson said. "You and I are made of the stuff that came from a supernova."