This fascinating metal has always influenced the human life, as a symbol of wealth; it has been considered an element with magical and divine properties. Its origin starts far, far away from our planet, even from the stars!
When the universe was originated 13.7 billion years ago by the Big Bang, there were only 3 elements there: hydrogen, helium and lithium.
It was due to the stars, through various nuclear fusion cycles, that heavier elements originated from the lighter ones: from hydrogen to helium, from helium to beryllium and, with a series of increasingly complex interactions, involving different atomic species at the same time, it was possible to obtain very heavy elements, such as gold.
However, not all the stars are able to generate it: just consider that a star with the same size of the Sun, towards the end of its life cycle, can originate elements like carbon, corresponding to atomic number 6, which means its nucleus is composed by six protons and six neutrons. A small result considering that the atomic number of gold is 79!
Only the stars exceeding the size of 10 solar masses (10M) are able to reach the pressures and temperatures necessary for gold formation.
Another possible process requires the collision of two neutron stars, celestial bodies with very high densities. During this phenomenon, a huge amount of energy is released, being able to originate the precious metal.
But, how can gold be present on our planet?
The elements that created the solar system come from the death of older stars.
Regardless of size, all the stars, at the end of their life cycle, increase their diameter so much, that they cannot be able to retain with their gravity the external layers, which are thus dispersed in space.
When a star reaches a mass over 10M, there is a state of imbalance that can generate a Supernova, an enormous explosion capable of wiping out most of the mass in interstellar space.
The dispersed material coming from different stars can aggregate into nebulae and, if sufficiently dense, they can rise, over time, to a planetary system, as happened, for example, to our solar system.
Gold is therefore a rather rare element in the universe, as well as on Earth.
Luckily, there are geological processes that can select it and concentrate it that allow humans to extract it.
By Stefano S