What is the main sequence?
The main sequence refers to the long period when the star shines steadily and brightly. Our Sun is now at the main sequence stage.
What is stellar evolution?
Stellar evolution refers to the stages in the evolution of a star as follows:
- The star begins as a cloud of interstellar material perhaps a light year in radius.
- The cloud contracts and also heats up for a few million years.
- A spherical star shape, called a proto-star, begins to emerge. The temperature is about 20000C.
- The proto-star begins heating up and the fusion reaction begins. The star flares up in a short interval of time and stars glowing. At this stage, the luminosity of the star may increase to several hundred times the Sun’s present luminosity.
- The star cools down to a steady equilibrium stage. The main sequence stage is reached and continuous for some ten billion years.
- The star starts growing and the luminosity starts decreasing.
- The star becomes a red giant and continuous in that state for a few hundred million years.
- The red giant starts shrinking. The luminosity increases.
- The star becomes a white dwarf and continuous to shine for a few billion years at the expense of its internal energy.
- The star exhausts all its internal energy and ceases to glow. The star has now become a black dwarf and reached the final stage of stellar evolution.
What happens to the radius of the star as it passes through the ten stages of evolution?
The radius of the star continuously decreases through the various stages except at the red giant stage when it temporarily increases.