Which are the most energetic events in the Universe?
That's the question. I know about gamma ray bursts, is there anything more energetic?
This question makes no sense unless "events" are somehow localized in space and time. Otherwise the obvious winners are global events like stellar evolution and cosmic speed-up.
@WillihamTotland Since dark energy (responsible for the speed-up) constitutes 68% of the universe, I'd say cosmic speed-up is the most energetic by definition.
@DmitryGrigoryev There's a lot of gravity involved, tho', and also a _lot_ of space. It might have the most _total_ energy, but per unit volume?
@WillihamTotland This is exactly the issue my first comment states. The question has little meaning unless constraints on time and space are defined.
@DmitryGrigoryev While I agree that the question could be refined, I feel as if an even moderately charitable reading of the question as stated can give an answer (probably 'Hypernovae', but I digress). Global events are processes that are so slow and so large scale that a novice could hardly be blamed for failing to take them into account.
Wikipedia has a page on this:
I would have guessed the recently observed merging of 2 black holes, which, while just hard to detect gravity waves, in terms of energy it was about the equivalent of the entire rest mass of our sun. Two large (but not super-massive) black holes each about 30 solar masses, merged and released about 3 solar masses in energy in gravity waves. That's a huge amount of energy.
I'd have guessed wrong though, as an observed gamma ray burst was bigger. (see link above for precise estimates).
In theory, since I assume you're talking about localized events, when 2 galaxies merge and their super-massive black holes collide, that's probably, hands down, the most energetic local event, far surpassing the largest gamma-ray bursts. Gravity waves might not be what people think of as energetic, but they can be enormously so. If you're talking more typical "bright flash", photons and accelerated particles, then the winner would be the largest gamma ray bursts. Hypernova's are up there, but not as large as the largest Gamma-ray Bursts.
Now if you want to get flexible on what "local" means. The gravitational energy of two large galaxies falling towards each other might get you a larger number, but I'm a little fuzzy on whether that qualifies as a local event", which I've built this answer on.