Describe what triggers a star leaving the main sequence:
The general theory why stars prefer to leave the main sequence is that when the Hydrogen fuel core is being consumed, energy is being released; permitting the radiant energy to pass through the star’s outer core, making it to expand more and eventually, stars leave the main sequence.
Explain how a star initially turns into a Red Giant:
As the stars continue to expand and increase in size, the expansion of the outer layer of the stars causes the surface temperature to fluctuate, leading these stars to exhibit a dark red color. The stars’ luminosity also increases due to an increase in its size and diameter. By increasing its luminosity, the stars brightened and expand into a so-called Red Giant Stars.
Be able to identify on a CMD where Red Giant Stars are located:
A cluster of stars can form Color Magnitude Diagrams (CMD). In general, there are two types of star clusters, the Open Star Clusters which can be found in the Milky Way Galaxy, and the Globular Star Clusters, which lives in the ‘halo’ of the Milky Way Galaxy. Hence, Red Giant Stars can be identified and classified according to its location in the galaxy, as whether it can be either an Open or Globular star clusters.
Describe what occurs in the core of a star once it becomes a red giant:
In the transition state of stars and the Red Giant Stars, the core of the stars shrinks as it expands, making it hotter and prone to Helium fusion. As the Helium fuel becomes fused in a rapid state, a blast of radiant energy is being released, causing the outflow of material. Considering the state of the Red Giant Stars, as Helium fusion continues to run out, the core collapse and becomes even hotter compared to its transition state. Eventually, the core starts fusing Carbon to Oxygen, then into Neon, Magnesium, Silicon, and finally, the Iron element. The accumulation of a mass of star will depend on the number of layers that the Red Giant Stars penetrated, causing more massive stars to evolve faster and turn into larger giant stars.
What happens to the material in the outer layers of a star as it evolves as a Red Giant?
As the core responds to the loss of energy being released by continuous contraction, the outer layers respond the other way by expansion. Aside from the expansion of the outer layers, their temperature also decreases as the result of the expansion.