discuss stellar evolution(briefly describe each stage). what forces are opposing one another throughout the life of a star and how do they influence the various stages in the life cycle of a star?
It depends on how big the star is. Here is an article on it:
http://en.wikipedia.org/wiki/Stellar_evolution
thank you Damon for the help on both questions.
Stellar evolution is the process that describes the life cycle of a star from its birth to its death. It can be divided into several stages, each characterized by different physical processes and forces at play. Let's briefly discuss each stage:
1. Protostar: A protostar is formed from a dense cloud of gas and dust that collapses under its own gravity. As the protostar contracts, its core temperature increases, and nuclear reactions begin.
2. Main Sequence: The main sequence is the longest stage in a star's life cycle. It occurs when the core of the star reaches a temperature and density capable of sustaining nuclear fusion. The opposing forces at play during this stage are gravity, which wants to collapse the star, and the outward pressure generated by fusion, which tries to expand the star. These forces achieve equilibrium, resulting in a stable star.
3. Red Giant/Supergiant: When a star depletes its hydrogen fuel in the core, the balance between gravity and fusion is disrupted. Gravity takes over, causing the core to contract. The outer layers expand, and the star evolves into a red giant (for low-mass stars) or a red supergiant (for high-mass stars).
4. Planetary Nebula/SuperNova: For low-mass stars, the red giant phase ends with the expulsion of its outer layers, forming a glowing shell of gas called a planetary nebula. In contrast, high-mass stars undergo a violent explosion known as a supernova, where the outer layers are expelled with tremendous energy. These events mark the end of the star's life.
5. White Dwarf/Neutron Star/Black Hole: After the expulsion of its outer layers, the remaining dense core of a low-mass star becomes a white dwarf. White dwarfs are held together by electron degeneracy pressure, as the outward pressure of electrons resists the collapse of gravity. In contrast, high-mass stars may form either a neutron star or a black hole, depending on their initial mass.
Throughout the life cycle of a star, the forces of gravity and fusion oppose each other. Gravity pulls inward, compressing the star under its own weight. In contrast, fusion reactions in the star's core generate an outward pressure, pushing against gravity. The balance between these forces determines the stability and lifespan of the star. When the fuel supply for fusion runs out, gravity gains the upper hand, leading to further stages of stellar evolution.