Page 8, Stars II

Page 8, The Stars II: [Previous Page] [Next Page] [Lecture Notes] [Class Home Page]

Evolution of Stars more Massive than our Sun

The Sun, once it's created a Helium core, is not able to evolve anymore. This is because the core does not have enough mass (and thus pressure) to create temperatures high enough to begin fusion reactions of Helium in to Carbon. However, In stars several times the mass of the Sun, they DO.

For stars up to 8 times that of the Sun, they will pass through a Planetary Nebula stage, just like our Sun.
Stars that begin their lives as A stars (mass range from 1.5 to just about 3 times our Sun mass) will have enough mass in their central cores to collapse and fuse Carbon into Neon or possibly Magnesium
2 ¹²C --> ²⁰Ne + ⁴He or ²⁴Mg

B stars (having mass range from 3 to 15 times our Sun) will fuse Neon or possibly Oxygen, into Magnesium, Sulfur and Silicon. All of this occurs at various stages in the ever shrinking, hot core.

Now, O stars.. They have the highest initial masses of all. O stars will fuse elements all the way to Iron at their cores! For the high mass B and all O stars, they can not become white dwarfs. Their central cores are entirely too massive. As we will soon see, an entirely different fate awaits them.