What fundamental astrophysical process occurs exclusively under intense central core conditions?

Nucleosynthesis (creation of elements heavier than hydrogen and helium)

The creation of elements heavier than the lightest ones, hydrogen and helium—a process fundamentally known as nucleosynthesis—requires the extreme conditions found only deep within a star's core. These conditions involve the immense pressures and temperatures, such as the $15$ million K found in the Sun, which are necessary to force atomic nuclei to overcome their mutual repulsion and combine. Without these intense central conditions, the nuclei lack the required kinetic energy to fuse, meaning that the creation of heavier elements like carbon, oxygen, and iron, which sustain life and form rocky planets, is entirely dependent on the star's internal furnace operating at peak intensity.