Gold is a precious metal that is very well valued by humanity. For thousands of years, humans have searched a way to transform materials into gold, without success. Thanks to scientific and technological progress, we nowadays know the mechanisms through which gold is created.
The origin of gold
For a long time, scientists have been able to determine where most of the elements of the periodic table come from. The Big Bang created hydrogen and helium, the two lightest and most abundant elements in the universe. Stars were then responsible to synthesise heavier elements (such as carbon, oxygen, …) through a process known as nuclear fusion, which consists in fusing atoms to create heavier ones. This produces a tremendous amount of energy. In the last years of their lives, stars create the most common metals, such as aluminium and iron, which are then scattered through space in enormous explosions known as supernovae.
During many decades scientists thought that it was in these explosions that the most heavy and rare elements were created, including gold and uranium. However, this theory ended up being discarded, because supernovae don’t have the necessary energy to form such heavy elements. The origin of gold comes in fact from the bodies left behind by the supernova explosion: neutron stars.
This type of stars are so dense that they contain the mass of 1,5 Suns in a sphere 20 kilometres in diameter. As Einstein’s equations describe, a pair of neutron stars that orbit one around the other will end up colliding. In these collisions is where the heaviest elements of the periodic table are created.
Observing the creation of gold
Neutron stars collisions create an enormous amount of gravitational waves (waves that travel through the fabric of space), that we can detect thanks to gravitational wave detectors, such as LIGO. Once it is confirmed that a collision of neutron stars created the waves, astronomers direct their telescopes to the region of space they come from.
The light that gets to us from this event can be analysed. This shows us which elements are present in the collision.
For example, on the 17th of April 2017, a collision between two neutron stars was observed, which create 10 times the mass of the Earth worth of gold.
The gold that is nowadays found on the surface of the Earth arrived billions of years ago through the impact of asteroids that contained this precious metal.