The fusion magic of our Sun’s energy

Here’s how you create energy: take 600 million tons of hydrogen and heat it to about 10 million degrees or more. After reaching the desired temperature, you are left with 596 million tons of helium, and the rest, 4 million, evaporates.

And what evaporates is pure energy. At least that’s how it is on the Sun. Every second, the Sun delivers so much energy into space that only a fraction reaches the Earth, and we live on that energy.

It is an economical process. If the Sun was made of coal, all the firewood would have burned up in two or three million years even before the Earth was formed. And instead of our beautiful planet, which would be turned into smoldering ashes, a rocky boulder would be orbiting, frozen from the cold. And there certainly wouldn’t be anything alive on it.

But the Sun is not made of coal and has a much, much more economical way of heating, such that it has been steadily shining and radiating its heat for five billion years, and it will continue to do the same for as long before really dramatic things happen to it.

But why does this process of converting hydrogen into helium generate energy?

The answer is found in the most famous equation of physics: energy is mass times the speed of light squared (which is written E=mc2 as you know), which means that energy and mass are equivalent and can be transformed into each other according to the given formula.

You should pay attention to c2 because it says that even a small amount of mass can be turned into a huge amount of energy! C is the speed of light, so 300,000 km/s and then squared!

But how does this alchemy – turning hydrogen into helium, happen?

Several scientists paid attention to the solution of that problem, and one of the early ones was Fritz Houtermans, a Danish-Austrian-German nuclear physicist who lived from 1903 to 1966.

He started from the already existing assumption that in the Sun, which normally consists primarily of hydrogen, then significantly less of helium, and then of everything else in negligible, although important, amounts, energy is created through the fusion of hydrogen into helium.

That was a good initial guess, but no one knew how the fusion happened. What was known was that during the fusion of one kilogram of hydrogen into helium, energy that is equal to the energy of burning 100,000 tons of coal is obtained!

The problem is that fusion cannot happen spontaneously and that certain conditions are necessary for that process: very high temperature and very high pressure.

Here’s a simplified version of the process.

The hydrogen nucleus consists of one proton, and the helium nucleus consists of two protons. In order to obtain helium, we need to combine two hydrogen nuclei, i.e. two protons. Well, but the problem is how to do it when the protons are positively charged, and the same charges repel each other!

Well, this is possible if two protons are very close to each other because then they are affected by a strong nuclear force that is much stronger than the repulsive electromagnetic force.

The strong nuclear force is actually the strongest force that exists, except that it is short-ranged and only acts within the atom. And how close must the protons be to be captured by the strong nuclear force?

Houtermans calculated it and found that such a distance is one billionth of a millimeter! So, when two protons get so close to each other, they connect, they fuse into one nucleus, which is the helium nucleus – with a loss of mass that is transformed into energy.

The conditions necessary for this process to occur exist on the Sun. It is a huge sphere 1,300,000 kilometers in diameter that has high pressures that cause high temperatures. In such conditions, atoms are crushed, protons run wild and rush, they collide with such force that they – join together.

This is just a very simplistic way of explaining fusion logic.

But the point is that nature has created a mechanism in which a small amount of matter is efficiently converted into a huge amount of energy!