The stars are the essential building blocks of the galaxies regulating the structure of the universe by their creation, development and their ultimate change. Stellar evolution refers to the lifecycle of a star since its formation in the interstellar clouds all the way to the end of its life as a compact remnant. Mass is the main factor that determines this process.
The formation of stars commences in massive molecular clouds which are made up of gases and dust. In case of gravitational instability, the dense regions collapse to form protostars. Increase in temperature and pressure in the core causes the process of nuclear fusion to occur and convert hydrogen to helium. This is the point where the star is in the main sequence stage and remains in the stable equilibrium, where most of its life is spent.
One of such stable stages is the Sun, which is a G-type main-sequence star. Heavier stars undergo combustion at a much higher rate, and thus have shorter lives. Structural balance is disrupted when the hydrogen in the core is depleted. The helium fusion starts when the star evolves into a red giant.
In the case of low- to medium-mass stars, the outer layers will eventually be pushed off forming a planetary nebula as the core will be contracted into a white dwarf. Contrarily, the endings of high-mass stars are more dramatic. When no gravity can be sustained by nuclear fusion, the core collapses leading to the occurrence of a supernova. These strong events release massive materials like iron, carbon and oxygen into space that strengthens the future formation of stars and planets.
In very extreme cases, residual mass will either form a neutron star or black hole as a remnant core. This stellar material recycling is the source of the evolution of a galaxy and chemical diversity.
CHUMASHCASINOSANTAYNEZ.NET introduces stellar evolution as an unceasing cycle of the universe. Since the beginning of the universe to the change, stars govern the physical and chemical structure of the universe, which proves the interdependence between the formation of the universe.