Complex sentence: The final stage in the stellar nucleosynthesis process is the silicon burning process that results in the production of the stable isotope iron-56, an endothermic process that consumes energy, and so further energy can only be produced through gravitational collapse.
Split into simpler sentences: The final stage in the stellar nucleosynthesis process is the silicon burning process that results in the production of the stable isotope iron-56. Fusion cannot proceed any further except through an endothermic process, and so further energy can only be produced through gravitational collapse.