You're looking at the most powerful X-ray blast ever recorded. You can be thankful we've an atmosphere. This thing was so strong that—even 5 billion light-years away—it overwhelmed the Swift observatory's instruments. Nobody knows what it really was.

The Swift mission's chief scientist David Burrows, at Pennsylvania State University, is bewildered by the findings.

[The software] basically threw up its hands and said, 'Something must be wrong, because the data doesn't make sense.' We're very puzzled – we don't understand it yet. Every once in a while something comes along that's completely unexpected and this is one of them.

The explosion only lasted a few seconds—with Swift receiving 143,000 X-ray photons per second—but the glow continued for 10 minutes after that.

Astronomers don't know exactly what's the origin, so here are my scientific guesses: a) The Kree and the Skrull finally annihilated each other using twin versions of the Ultimate Nullifier; b) Klaatoo bought himself a new camera; c) Galactus has some serious intestinal problems.

Alternatively, they think it may be the collapsing of a giant star to form a massive black hole. [Swift mission team via New Scientist]