Asked by: Bill Dobell, London
Gold owes its status as a precious metal to its rarity: all the gold mined throughout history would fit into a square box with sides of around 20m in length. That’s not because of a failure to mine more. Gold is rare throughout the Universe because it’s a relatively hefty atom, consisting of 79 protons and 118 neutrons. That makes it hard to produce, even in the incredible heat and pressure of the ‘chemical forges’ of supernovae, the deaths of giant stars responsible for creating most chemical elements. There’s even doubt that supernovae are up to the job. Recent research suggests that even more violent events, such as collisions between neutron stars – the ultra-dense cores of dead stars – may be needed. No wonder the stuff is so expensive.