Solar death

Describe the stages our Sun will undergo moving off of the main sequence. What event marks the beginning of the movement off of the main sequence? What is a white dwarf? A black dwarf? Stage 8 (The Subgiant Branch) marks the beginning of the star's departure from the main sequence. The Subgiant Branch: As the stars become older, there will be an increase in helium richness. Due to the increase in Helium richness, the content of hydrogen slowly subside. The maximum temperature in the core of the star causes helium content to expand and hydrogen content to deflate. The deflation of hydrogen in the center of the star causes nuclear fire to subside and the burning to move to the higher levels. Due to the change in content of the star’s interior the average surface temperature remains the same, but the luminosity and the radius increase slowly. The temperature and the luminosity of the stars continue to change as the time passes. The stars radius increases there times the radius of the sun and it is roughly in horizontal path from the main sequence. This is called Subgiant Branch. The Red-Giant Branch: At this stage the star is away from the main sequence and is not in equilibrium anymore. The helium core of the star is shrinking, and the rest of the star core is also unbalanced. Hydrogen is fusing into helium at an ever-increasing rate.  The hydrogen Shell is burning so fast in this stage that the luminosity is many hundreds of times the solar value and the radius is 100 times of the sun. The almost vertical path followed by the stars in these stages is known as red giant branch of H-R diagram. Helium Fusion: When the temperature rise to〖 10〗^8 K in the core of the star, the helium core start to fuse through triple-alpha process. This happens a few hundred million years after solar mass star leaves the main sequence. Back to Giant Branch:  The stars that have just left the main sequence and the stars at this stage are similar in nature except the later ones have two shells. When the helium in the core fuses to carbon, the core becomes hotter and hotter, and the helium burns faster and faster. The carbon core grows in mass but shrink in radius, forcing an increase in temperature and luminosity in the hydrogen-burning and helium-burning shells. A Planetary Nebula: At this stage, the carbon burning becomes unstable and the helium burning shell is subject to a series of explosive helium-shell flashes caused by the pressure in the helium burning shell. No energy is generated any longer from the carbon core. Whatever fuel is left heats up and become ultraviolet radiation, which causes to glow the outer layer. White Dwarfs: A white dwarf is a star with a high surface temperature with a glowing white light. There is no more burning in the core of these stars. They only shines due to its stored heat. Black Dwarfs: The white dwarf turn into black dwarf after it cools and becomes dim. Black dwarfs are about the size of the earth