How about a supernova that's 570 billion times as bright as the sun? Thankfully, it's 3.8 billion light years away (Which also means it happened 3.8 billion years ago).
Thankfully because you wouldn't want to be close to it - the gamma ray burst may have sterilized planets in systems closer to the explosion.
And no, we don't know how such a big supernova happens yet.
As a side note, remember the star that's so weird that people have been citing "aliens" and "dyson sphere" in serious competition? They appear to have eliminated the most likely explanation of a comet swarm as they've now discovered that in addition to the flickering the star is steadily losing luminosity...
So, more things we don't know.