The beginning of the universe only saw the creation of hydrogen, helium and some other light elements. But we’re clearly made of much weightier particles, so where did all of those elements that surround us, and are contained within us, come from? How did carbon, that’s so important for life, reach our little planet?
The answer is written in the stars – those huge nuclear reactors whose deathly smouldering temperatures are responsible for the creation of life-giving elements. This violent heat rips the electrons from the atoms contained within a star’s core and throws around the remaining nuclei with such high energy that even the repulsion between the positively charged protons can’t keep them apart. They become so close together that the superglue responsible for keeping nuclei intact comes into play – this force was named ‘the strong nuclear force’ – and an atom is created that contains a different number of protons to its parents, making it a different element entirely. It may seem like a very generous act, stars providing all this energy to give us the gift of elements, but, in fact, it is this process of fusion that keeps stars twinkling happily for millions of years.
It is this change in binding energy that can release the colossal amounts of energy needed to power the furnace within a star.
Elements can be fused together again and again to produce elements of increasing atomic number and weight, and this process will be able to produce energy until the element becomes as heavy as iron, which has an atomic number of 26. This is because fusing small nuclei together creates a more stable element, which means that the energy holding together the nucleons is stronger than the energy that was holding its parents together. This increase in stability is directly related to an increase in the binding energy of a nucleus (the energy that would be needed to rip that nucleus apart) and it is this change in binding energy that can release the colossal amounts of energy needed to power the furnace within a star.
The death of a high mass star is a even more cataclysmic cosmic event. Like the log fire that we all dream of in our cold student houses, a star can only burn bright until all its fuel, in the form of lighter, fusible nuclei, runs out. When this happens, a star’s core will begin to cool, causing it to contract and throw off its outer layers. The star will keep on contracting, pushing together the protons and electrons until they are forced to react to produce neutrons, along with neutrinos (which have the good sense to escape).
The temperatures reach such monstrous heights during this process that it becomes possible for elements heavier than iron to be produced.
The density of the star will continue to increase until the neutrons cannot be forced any closer together, causing such an increase in gravitational pull that the outer layers are pulled back towards the core. But when this layer meets the rigid core, it rebounds back into space to create the enormous explosion that is a supernova. The temperatures reach such monstrous heights during this process that it becomes possible for elements heavier than iron to be produced.
It is not just this miraculous act of creation that we have to thank stars for. Dying in such a violent way enabled the elements to journey across the cosmos and land on our planet as ready-made building blocks for us to make this planet home. With the life-cycle of a star lasting more than millions of years, it is clear to see that the stardust that makes up every atom in our body came a long way, across vast expanses of time and space, to stumble upon the creation of human life.