Elements heavier than iron are primarily formed through processes that occur in the extreme environments of stellar explosions called supernovae and in the merging of neutron stars.
In the core of massive stars, nuclear fusion reactions produce energy by fusing lighter elements into heavier ones. However, this fusion process stops at iron because it requires an input of energy rather than releasing it. Once a massive star has exhausted its nuclear fuel and can no longer support its own weight against gravitational collapse, it undergoes a catastrophic supernova explosion.
During a supernova, the intense temperatures and pressures generated in the core of the star enable the rapid fusion of lighter elements, including iron, into heavier elements through a process called neutron capture. Neutrons are rapidly absorbed by atomic nuclei, increasing their atomic mass and creating unstable, neutron-rich isotopes. These isotopes subsequently undergo radioactive decay, transforming into elements beyond iron, such as gold, platinum, uranium, and many others.
Additionally, the merging of neutron stars, which are incredibly dense remnants left after a supernova, can also contribute to the production of heavier elements. When two neutron stars collide, the extreme conditions generate intense heat, pressure, and neutron capture processes, resulting in the creation of a wide range of heavy elements.
These stellar explosions and neutron star mergers distribute the newly synthesized heavy elements into the surrounding space. Over time, this enriched material can become part of interstellar clouds, where it may eventually form new stars, planetary systems, and even life as we know it.
In summary, while fusion in stars cannot produce elements heavier than iron, supernovae and neutron star mergers provide the necessary conditions for the creation of these heavy elements, enriching the cosmos with a diverse range of atomic building blocks.