So I did some quick calculations:
The energy required to coalesce a ball of material that's uniform in density with properties of Earth is something like 2 * 10^32.
The energy released in Earth's formation is higher, because the denser materials sunk into the core while lighter ones floated up. So if you want to blow up Earth (or Alderaan), you'll need to put in at least that much energy. Let's call it 10^33 J.
But you wouldn't build a Death Star just to blow up one planet! You'd build it so that it could blow up multiple ones! Like 10
So let's give it an energy content of 10^34 J.
So when the death star blows up and all that energy just goes off, what temperatures would it attain?
Well, I don't know what it's made of, but if we assume a solid sphere of 170 km, made of iron, that energy is already enough to heat it up to
100 billion Kelvin!
You can get gamma rays easily from 10 billion Kelvin up, so this one would be quite spectacular. When 500 km from the surface of the planet, it'd be quite the bang
Don't you just love the science behind killing Ewoks? :lol:
But look at the bright side! It's not just the Ewoks! Everyone on Yavin IV is dead as well!