What are the different stages of the life cycle of an average star
The life cycle of an average star can be divided into the following stages:
1. Nebula: A star begins its life as a nebula, a cloud of gas and dust in space. Gravitational forces cause the nebula to condense and collapse due to the force of gravity.
2. Protostar: As the nebula collapses, it forms a protostar - a dense and hot core at the center. The protostar continues to accumulate more matter from the surrounding gas and dust.
3. Main Sequence: When the temperature and pressure at the core of the protostar become high enough, nuclear fusion begins. This initiates the main sequence phase, where a star enters a stable phase of its life, converting hydrogen into helium in its core. This phase can last for millions to billions of years.
4. Red Giant or Super Giant: As the hydrogen fuel in the core starts to deplete, the star begins to expand and becomes a red giant or a super giant, depending on its initial mass. This phase is characterized by the fusion of heavier elements like helium and hydrogen in different shells around the core.
5. Planetary Nebula: In the last stages of a star's life, it expels its outer layers of gas, creating a glowing shell known as a planetary nebula. The core of the star, which is now a white dwarf, remains behind.
6. White Dwarf: The remaining core of the star, after the expulsion of outer layers, becomes a white dwarf. It is small, extremely dense, and no longer undergoes nuclear fusion. Over time, it cools and fades away gradually.
7. Black Dwarf: Theoretical models suggest that a white dwarf will eventually cool down completely, becoming a black dwarf. However, as the universe is relatively young, no black dwarfs have been observed yet.
It is important to note that stars more massive than the Sun follow a different life cycle, including stages such as supernova, neutron star, or black hole formation.