How does the relative duration of the silicon-burning stage compare to the star's main sequence life?
The silicon-burning stage can last less than a single day, a stark contrast to billions of years.
The duration of any fusion stage in a massive star is inversely proportional to the energy required to overcome the electrical repulsion of the atomic nuclei involved. As fusion progresses up the ladder to heavier elements—from hydrogen to helium, carbon, neon, oxygen, and finally silicon—the time spent in each subsequent shell burning stage dramatically shortens. The silicon-burning phase, which precedes the formation of the inert iron core, is extremely brief, sometimes lasting less than 24 hours in the most massive stars. This frantic rush contrasts sharply with the billions of years spent steadily fusing hydrogen into helium during the star's main sequence existence.
