ReutersOn Wednesday, Jan. 6 (local time), North Korea claims it set off a hydrogen bomb.
While experts investigate to see if that's true, the US remains unconvinced. But it's clear some kind of nuclear blast happened.
A hydrogen bomb is different than a regular atomic bomb, like the ones the US dropped on Japan near the end of World War II.
Collectively, the two A-bombs that the US detonated over Hiroshima and Nagasaki killed more than 200,000 people.
But an H-bomb is an entirely different beast. It can be up to 1,000 times more powerful than an A-bomb, according to nuclear experts.
Fission vs. fusion
North Korea tested atomic bombs back in 2006, 2009, and 2013. Their blasts were created using fission — the splitting of atoms into smaller ones. Heavy, radioactive forms of elements like plutonium and uranium are especially susceptible to do this.
Every fission or split of an atom releases a huge amount of energy. It's the same thing nuclear power plants use to generate energy for your home.
However, if the atoms are quickly squashed very close together, a runaway effect can happen that rapidly splits many, many atoms almost all at once — and releases a catastrophic blast of energy.
Below is a Reuters illustration that shows two different models of atomic bombs. The goal of each is detonate traditional explosives (tan) to squeeze a fissionable material, like plutonium-239 (teal) or uranium-235 (yellow), into a "supercritical" mass that splits atoms like crazy.
The device on the left is an implosion-type fission bomb, like the Fat Man bomb detonated over Nagasaki, and it compresses everything inward.
The one of right is a gun-type fission bomb, like Little Boy detonated over Hiroshima, which shoots the missing piece of a nuclear core right into the center to make it go supercritical:
Hydrogen bombs do something even more extreme.
They rely on combining two or more atoms together in a reaction called fusion. Fusion is what powers stars like our sun to make them so hot and bright, to give you an idea of the potential power of a fusion bomb.
The reason experts are so skeptical about North Korea's hydrogen bomb is that fusion is hard to do on Earth; those weapons are very complex, difficult to make, and hard to detonate in exactly the right sequence.
Yang Uk, a senior research fellow at the Korea Defence and Security Forum, told The Guardian that if the test was real, then North Korea likely tested a "boosted" fission device, not an actual fusion device.
All it takes is a look inside these bombs to understand the skepticism.
Below is a second graphic showing a boosted atomic bomb and a hydrogen bomb. A special form of "heavy" hydrogen or deuterium (green), is key to both weapons. It causes more fissionable atoms to split, and thus release more energy all at once.
In order to trigger fusion, however, you need a ton of energy — which is why a fission bomb has to detonate first. So H-bombs are really made of two bombs: a fission bomb and a fusion bomb:
Inside an H-bomb, a "boosted" fission bomb releases a blast of powerful X-ray radiation, which is focused precisely onto the fusion bomb. (This happens before the shockwave can blow apart an H-bomb, by the way, since X-rays travel at light-speed and blast shockwaves do not.)
That X-ray blast then sets off the fusion bomb, creating an explosion powerful enough to merge a bunch of atoms, convert some of that material into pure energy, and trigger a blast that's frighteningly more powerful than an atomic bomb's.
Here's the full Reuters graphic that compares all of the bomb types: