At the end of its lifespan, a massive star (at least 8 times more massive than the Sun) fuses iron molecules in its core. Since nuclear fusion reactions don't release any energy from iron, the core stops producing the heat and pressure needed to support its own weight. Consequently, the core rapidly collapses under its gravity.

2. Core Collapse

As the core collapses, the inner core rebounds off the outer core, creating a shock wave. This shock wave travels outward through the star's layers.

3. Rebound and Explosion

The shock wave from the core bounce travels through the star at supersonic speeds, but it encounters resistance from outer layers of the star, which are still collapsing inward. This slows the shock wave, causing it to heat up and produce more thermal energy. Eventually, the thermal pressure generated within the star exceeds gravitational forces and causes the star to explode in a supernova.

4. Shock Wave and Elements

The supernova explosion propels the shock wave and the star's outer layers into space. The energy from the explosion causes heavier elements like iron and uranium to be synthesized in the star's core through nuclear processes and scattered into the surrounding space. These elements eventually condense into dust and other cosmic materials, contributing to the formation of new stars and planets.

5. Supernova Remnant

After the supernova explosion, the remaining core of the star is extremely dense and becomes either a neutron star or a black hole, depending on its mass. The expanding debris creates a supernova remnant, which is a region in space filled with expanding gases, dust, and other remnants of the exploded star.