What do massive stars create during their explosion?

During their explosion, specifically during the process known as a supernova, massive stars are responsible for creating all elements above iron. This is due to the nuclear fusion processes that occur in the cores of these stars during their life cycles and the subsequent explosive events at the end of their lives.

In stellar nucleosynthesis, elements up to iron are created through regular fusion processes. Iron has the highest binding energy per nucleon, meaning that fusing iron does not release energy; instead, it requires energy. Therefore, the fusion of heavier elements such as gold, lead, and uranium occurs predominantly during the supernova explosion, where the extreme conditions allow for rapid neutron capture processes (known as the r-process).

This is why the formation of elements above iron is directly linked to the explosive event of a supernova, as these events have the necessary energy and conditions to produce these heavier elements, dispersing them into space and contributing to the cosmic abundance of elements.