What element fuses in massive star cores up to the point fusion ceases?

Iron (Fe)

Massive stars, exceeding eight times the Sun's mass, follow a highly energetic evolutionary path where they can fuse progressively heavier elements in nested shells due to their immense gravitational weight. This process continues through stages such as hydrogen into helium, carbon into neon, and so on, building up elements layer by layer. However, this process terminates abruptly when the core becomes composed primarily of iron ($ ext{Fe}$). Fusing iron is fundamentally different because it does not release the necessary energy to counteract gravity; instead, fusing iron consumes energy. Once this cosmic dead end is reached, the star instantly loses its primary energy source, leading to catastrophic gravitational collapse.