The structure of a star is a peculiar thing. It s a massive ball of gas that gravity wants to compress, but it s kept inflated constantly because it s a nuclear bomb that blows outward. It s a balance that allows a very long life span. But as a star ages, it s hydrogen fuel runs out. When this happens, the force of the constant nuclear ignition is no longer enough to blow back all of the star that wants to collapse upon itself.
Gravity wins and the resulting catastrophic collapse overwhelms the limited space it occupies.
If you re standing nearby, there s not much difference, in practical terms, between an implosion and an explosion. You see both in the supernova that results from the death of a star. In this process, all kinds of fusion reactions happen to the hydrogen and helium. Denser atoms are forged as the star collapses and everything gets smashed together with forces that can only be imagined. When all of this dense debris is cast off in the explosion, heavier elements are strewn throughout the universe.