The Sun, our closest star, is crucial for the presence of life on the Earth, thanks to the light and heat that it emits. The universe is inhabited by trillions of stars more, that light up our night sky, and with which we can obtain incredible images of the cosmos. But, how can stars produce so much light and energy?
Stars are enormous spheres of gas mainly formed by hydrogen and helium. Gravity in these bodies is so intense that in their nucleus takes place a process we call nuclear fusion, which is responsible for all the energy that stars produce.
What is nuclear fusion?
Nuclear fusion consists of the fusion of atomic nuclei, to form a heavier one. This process releases an enormous amount of energy. The two main elements that are fused at the centre of stars are hydrogen and helium. As we have explained, the fusion of these atoms makes the Sun and all the other stars shine.
This process of nuclear fusion is possible thanks to the intense gravitational field of stars. The atoms at the nucleus of a star are subject to extreme pressures and temperatures. This makes it possible for the hydrogen nuclei to overcome their natural repulsion and merge, to form a helium nucleus.
Once a star has exhausted its hydrogen supply, it starts fusing helium atoms to form heavier elements, such as carbon and oxygen. This process continues, forming in this way the elements of the periodic table. However, this process stops when iron is reached: the fusion of this element doesn’t release energy any more, but it consumes it, which makes the star collapse under its own weight, in the form of a supernova.
The significance of nuclear fusion
Apart from making stars shine, nuclear fusion also prevents the stars from collapsing due to gravity. The light and heat that emit the fusions of atoms counteract the gravitational force, making it possible for the star to continue existing. In fact, it is at the moment when the star can’t produce more energy that it disappears in a great explosion.
After the Big Bang, which represented the creation of the universe, only hydrogen, helium and a little bit of lithium existed. Thanks to nuclear fusion nowadays exist all the other heavier elements, which makes it possible for life to exist on Earth.
Finally, nuclear fusion represents an almost unlimited form of energy that doesn’t produce any waste. For this reason, the first nuclear fusion reactors are being constructed, for many years, in order to have a clean energy source that would enable to supply the energetic demand of all the population.