Stars are hot balls of gas. They are held together by their own gravity. The nearest star to the earth is the Sun. They give out light of their own due to nuclear reactions.
What are the stages in the Life Cycle of a Star?
- The life cycle of a star is determined by its mass. The larger the mass of a star the shorter will be its life cycle. The life of a star ranges from a few million years to a billion years, depending on the mass.
- It is believed that stars are born from collapsing dense clouds of dust and gas found in spiral galaxies. These clouds are called molecular clouds or nebulae, and are made up of 97% hydrogen and 3% helium.
- When the nebula collapses under its own gravitational force, it breaks apart and results in the formation of a dense sphere called a Protostar.
- These protostars are dense bodies of dust and gas which have not begun to generate light. As the mass of each protostar increases so does its gravity, squeezing the core of the protostar harder.
- As the stars expand, they become less bright, due to the core running out of hydrogen and then helium. Then the star enters the main sequence or adult phase. A star remains in this phase for most part of its lifetime.
- A star leaves its main sequence phase when it runs out of hydrogen and starts fusing helium and other elements.
- Dim small stars are called red dwarfs. The fusion of hydrogen in them, takes place at a very slow rate and they are able to remain in the main sequence for billions of years.
- The low mass stars like our sun expand and become red giants. This red giant is a large star that is bright with a cool surface. This is formed when the star runs out of hydrogen. They are very bright because they are so large.
- Stars die in explosions called supernova. Supernova leads to the core compressing into a neutron star or a black hole.
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