It's like the difference between an explosion of TNT and a atomic bomb, but on a much larger scale.

Stars like our sun spend ~10billion years turning a portion of their mass into energy. Most stars are like ours, small, dim and weak in power output. Our sun will not go supernova and will not collapse into a black hole when it dies, it will simply go nova and end up as a dwarf star in a nebula.

But, now imagine two black holes each a billion times as massive as the sun turning all their mass into energy in a couple of seconds.

10billion years to convert 99% of the mass of the sun to energy versus 10 seconds to covert 2 billion times the mass of the sun to energy. Now it makes sense that the power output is more in one second than the whole universe put together.

Solar fusion is on the cosmic scale a very slow way to convert mass to energy. It's so slow that we humans have been 'on the brink' of harnessing it for power generation for decades.

Now imagine if we could build two nano-black-holes and let them collide....

> But, now imagine two black holes each a billion times as massive as the sun turning all their mass into energy in a couple of seconds.

Sure, lemme just take off my "good at socializing with apes and running for long periods of time after antelope" hat and put on my "Cosmological scale" hat.

Huh, I seem to have misplaced that one. And the one I'm currently wearing is oddly well affixed.

I think your numbers are a bit off. I am not sure about the exact numbers but I think the sun will only burn about half or so of its mass over its lifetime. Also the black holes we observed merging are stellar black holes with masses on the order of tens of solar masses, not galactic black holes with millions or billions of solar masses.

LIGO observed 3 mergers of stellar mass black holes on the scale of 20-60 solar masses, not billions.

I don't really understand this, especially "at any given time" part. Could someone elaborate?

The power (energy per unit time) emitted in the creation of gravitational waves by the source observed by LIGO was briefly greater than the light power emitted by all of the stars in the known universe. Basically, if the gravitational waves were in fact light (they're not), then they would have briefly outshone everything else in the universe put together.