Always shining on high, immutable, inexhaustible, boundless. The Sun is the engine of basically all atmospheric phenomena that occur on Earth. Its heat moves air masses and evaporates the water that forms clouds. In addition, it supports plants and other photosynthetic organisms, which in turn serve as food for other bacteria, archaea and animals, and has been doing so for billions of years. But where does it get its energy? What process is capable of maintaining a star like our Sun emitting energy at such high levels for such long periods of time?
Nothing more and nothing less than one of the most efficient processes in the universe: nuclear fusion. Its name is quite descriptive, since it consists of the fusion of two atomic nuclei to give rise to a larger one, releasing large amounts of energy in doing so. To give you an idea of the amount of energy that is released in nuclear fusion reactions, say that they are the foundation behind the Hydrogen Bombs, which are several times more powerful than those that exploded over the Japanese cities of Hiroshima and Nagasaki in August 1945. So, simplifying a lot, we can say that the Sun and any active star in the universe, is a huge hydrogen bomb, exploding millions of times per second. It does not fly through the air because its own gravity prevents it.
In fact, the core of a star can be understood as a region that is in a delicate balance . On the one hand we have the incessant force of gravity, which compresses all the gas and plasma that make up the star towards its center. The enormous pressures resulting from this compression raise the temperature to millions of degrees. On the other hand we have the countless mini-explosions resulting from each nuclear fusion process that takes place, explosions that try to blow up the star itself. As if it were a game of rope of epic scales, these two forces remain in balance during what we know as the “main sequence” of a star. But that is not what we wanted to talk about here.
Nuclear fusion needs very extreme and specific conditions in order to occur. This is why we only talk about it in the context of stars and atomic bombs. Nuclear fusion has a much more accessible sister, nuclear fission . Nuclear fission processes, which are what fuel a nuclear power plant or a nuclear bomb (such as those in Hiroshima and Nagasaki), can occur spontaneously. This is the opposite of fusion: a heavy atomic nucleus splits, giving rise to two new lighter nuclei and releasing energy in the process. But as I was saying, nuclear fusion is much more demanding. After all, what we are achieving with it is not exactly a small feat. Naturally, any two atomic nuclei (made up of a certain combination of protons, with a positive electric charge, and neutrons, with no electric charge) will repel each other. So much so that, under normal conditions, it will be impossible for us to put them together. When we try to do it , the electrical repulsion of the protons will prevent us . It will not be until we reach temperatures and pressures like those present in the core of a star that we will be able to overcome this electrical repulsion so that the nuclei come into contact, then the so-called strong nuclear interaction will dominate. This is much more intense than the electromagnetic repulsion, but only for very small distances, the typical size of an atomic nucleus.
In the Sun and the rest of the stars in the universe, nuclear fusion transforms 4 hydrogen nuclei (consisting of a single proton) into 1 helium nucleus (consisting of two protons and two neutrons) through an elaborate process that creates other isotopes of these elements as an intermediate step.
In atomic bombs these high temperatures are achieved with a small dose of nuclear fission. In other words, inside each atomic bomb there is a tiny nuclear bomb that fissions plutonium, uranium or another element to achieve the necessary temperature to unleash the full power of fusion. We could say that fission acts as a “fuse” for fusion in this type of bomb.
All this knowledge has led us in recent decades to try to create electric generators that use nuclear fusion as a source of energy . In these reactors, the extraordinary pressure and temperature conditions required are achieved by lasers, which heat the nuclear fuel, and by powerful magnetic fields, which keep the entire process confined to a safe area. These reactors should be able to generate large amounts of energy with little or no waste . Neither CO 2 nor radioactive waste. This is why there are several active projects working on this topic. Some progress has been made, although a reactor capable of producing more energy than has been supplied to run it has yet to be developed.
