Final answer:
The Sun stops producing heavier elements because its core does not reach the necessary temperatures and pressures to fuse elements beyond helium. The nuclear fusion process in the Sun's core, currently fusing 620 million metric tons of hydrogen into helium per second, will cease once the hydrogen fuel is depleted, preventing the creation of heavier elements.
Step-by-step explanation:
Why the Sun Stops Producing Heavier Elements
The Sun stops producing heavier elements such as iron because, as a main-sequence star, it does not possess the necessary core temperatures or pressures to fuse elements heavier than helium. The process of nuclear fusion requires increasingly extreme conditions for heavier nuclei to overcome their electrostatic repulsion and combine. In the Sun's core, nuclear fusion occurs at around 14 million kelvin, which is sufficient for combining hydrogen nuclei (protons) into helium. However, once the Sun has used up its hydrogen fuel, it will expand into a red giant, and despite its larger size, it still won't have the adequate core conditions to create elements heavier than helium. For elements such as iron to form, supernova events or components of massive stars are typically necessary, where extreme temperatures and pressures are present.
Throughout its main-sequence stage, the Sun continuously fuses approximately 620 million metric tons of hydrogen into helium each second. Yet, this transformation results in a loss of mass that eventually depletes the hydrogen fuel, causing the Sun's fusion reactions to stop before heavier elements can be formed. This defines the limit of nucleosynthesis in stars like the Sun, which will eventually lead to its transition into the post-main-sequence phases of its stellar lifecycle.