Answer :
Answer:
The process you're describing refers to the life cycle of a massive star, specifically what happens when it runs out of fuel for nuclear fusion in its core. Here’s a detailed breakdown:
1.Hydrogen Fusion (Main Sequence Phase): A star begins its life by fusing hydrogen into helium in its core. This process releases energy and keeps the star in a stable state called the main sequence. This phase can last millions to billions of years, depending on the star's mass.
2.Helium Fusion: Once the hydrogen in the core is depleted, the core contracts and heats up. This leads to helium fusion, where helium atoms fuse to form carbon through various nuclear reactions. For stars less massive than about 8 times the mass of the Sun, this is where fusion ends. The star expels its outer layers, forming a planetary nebula, leaving behind a hot core that becomes a white dwarf.
3.Heavier Elements Fusion (for Massive Stars): For stars more massive than about 8 solar masses, the fusion process continues after helium is exhausted. Successive shells of heavier elements (carbon, oxygen, etc.) fuse in the core, with each fusion stage occurring more rapidly than the last.
4.Iron Core Formation: Ultimately, a massive star's core becomes mostly iron, which cannot be fused into heavier elements through nuclear reactions. Iron accumulation signals the end of the star's ability to generate energy through fusion.
5.Core Collapse: Without the energy produced by fusion to counteract the force of gravity, the core collapses very rapidly — in a fraction of a second. This collapse happens because the core is no longer supported by the outward pressure generated by fusion reactions.
6.Supernova Explosion: The collapsing core reaches extremely high densities, triggering a shockwave that blasts outward. This explosion is called a supernova and can briefly outshine an entire galaxy. During the supernova, elements heavier than iron are synthesized and dispersed into space.
7.Remnants: Depending on the mass of the star's core left behind after the supernova, it can become a neutron star or, if the core is very massive, a black hole.
In summary, the scenario you described — a star running out of elements to fuse, leading to core collapse due to gravity — typically applies to massive stars (more than about 8 solar masses). This process is crucial in the formation of neutron stars and black holes, as well as in the production of heavy elements necessary for planets and life as we know it.