I'm not experienced in physics yet (if it helps I've covered as much as acceleration, momentum and energy transfer/chemistry ionic and covalent bonding) but I've heard that the way people compare destructive force of nuclear weapons by megatonnes or kilotonnes is wrong. This does seem to make some sense because the energy will turn into a mix of gamma (?) radiation, light radiation, heat radiation and other things, but is there an accurate way to compare nuclear weapon destructive force? Say, I wanted to compare today's weapons to Little Boy.
[Physics] Nuclear bomb power – theth
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I don't know about extracting mass-energy from inside the black hole; it seems pretty inefficient to me. Hawking radiation isn't that powerful (as well as still being highly hypothetical), but building a Dyson sphere around a star is better. Remember, black holes, are, well, black. If there was enough Hawking radiation, they would cease to be black and would shine like stars.
The efficient way to extract energy from a black hole is to extract its rotational energy. 20% 1 of a (rotating) black hole's mass-energy is in the form of rotational energy. This energy is not stored inside the black hole, rather it is stored in the swirl of space outside the black hole (in the Ergosphere). We can extract this energy by threading magnetic filled lines through the black hole. The swirl of space swirls the magnetic fields, and this swirl creates current (I'm not sure of the exact treatment of this, classically it would be some form of electromagnetic induction, but this isn't classical physics.). The current flows along the field lines and can be picked up.
Here's a picture from 1:
UPDATE: See this also.
1 Black Holes and Time Warps, Kip Thorne. Page 53.
The sun and all other stars are in effect thermonuclear bombs. If they get heavier than about 10 times the mas of the sun they eventually blow up as a supernova, so there is a limit to the size but it's a lot larger than anything we will ever build.
In the wikipedia article, the yield limits have to do with deliverability. It's no good having a huge bomb if you can only explode it in the factory where it's made. They're talking about "6 megatons per metric ton" so a 60 megaton bomb would weigh 10 tons. The article gives examples of delivery, with the limit being a 1.3Gt bomb deliverable by an Antonov An-225.
Best Answer
The so-called TNT equivalent of a nuclear weapon is an unambiguous way of quantifying how much energy is released by the nuclear weapon. There's nothing 'wrong' about it.
The only caveat is that the damage caused by, say, Little Boy versus 15 kilotons of TNT would not be identical despite having an equivalent yield (for various practical reasons).
Generally, 10-20% of nuclear yield is emitted in the form of ionizing or residual radiation, unlike conventional weapons. Related: effects of nuclear explosions.