Stellar Evolution
Introduction
Stellar evolution is the process by which a star changes over the course of time. This process is driven by the balance of gravitational forces and the internal pressure within the star. The changes in a star's properties are governed by the laws of thermodynamics, quantum mechanics, and nuclear physics.
Formation
Stars are formed within regions of higher density in the interstellar medium, known as molecular clouds. These regions are dense enough to collapse under gravity, forming a protostar. This initial stage of star formation is known as the star formation phase.
Main Sequence
Once a star has formed, it evolves onto the main sequence where it will spend the majority of its life. The main sequence phase is characterized by the fusion of hydrogen in the star's core. This process, known as nuclear fusion, releases energy that counteracts the gravitational force trying to collapse the star.
Post-Main Sequence
After a star has exhausted its hydrogen fuel, it leaves the main sequence and enters the post-main sequence phase. This phase is characterized by the fusion of heavier elements in the star's core. Depending on the star's mass, it may become a red giant, a supergiant, or a white dwarf.
Stellar Remnants
The final stage of stellar evolution is the formation of a stellar remnant. This can be a neutron star, a black hole, or a white dwarf. The type of remnant formed depends on the mass of the original star.