Life Cycle of a Star
The life cycle of a star: Main sequence/average star
Stars begin their life as a large cloud of dust and gas which is called a nebula. Eventually, a nebula will collapse under its own gravity. As the nebula collapses, it starts to spin and as the gas and dust spin faster and faster it gains more heat which is where a protostar is formed.
This gas and dust will continue to heat up for a very long time. When it reaches 15,000,000 degrees nuclear fission can occur in the core of the cloud. The cloud now begins to glow bright and contracts in size and becomes stable.
The star is now in the main sequence stage of its life, where it will spend millions-billions of years of its life. Our sun is in this sag of its life now.
As the main sequence star turns hydrogen to helium by the process of nuclear fission it will continue to glow. When the star uses all of its hydrogen and is no longer producing heat, t begins to become unstable and contracts by the process of nuclear fusion. The outer shell however which is still mostly hydrogen begins to expand. When it expands it cools down and glows red. The star is now in the red giant stage of its life.
When all of the helium has fused, the star will begin to cool and contract under the pull of gravity, where it will form a white dwarf which fades and changes color as it cools.
Massive star life cycle:
A star with much greater mass than our sun is called massive stars. Massive stars are born just like an average star. The star begins to turn hydrogen to helium by nuclear fission, making it glow. However since they are so big, this process takes much less time. The massive star then becomes a red supergiant.
Eventually, the core collapses causing an explosion that is called a supernova, which is extremely bright.
If the core survives this explosion it ill form a neutron star, however, if the core does not survive the supernova, it will form a black hole.