1. Stellar Evolution
Part 2
The fate of the Sun

2. Stars like our Sun
Stars with masses similar to our Sun fuse at a rate that allows them to “live” as main-sequence stars for about 10 billion years.
Then they run out of Hydrogen in their core
Hydrostatic Equilibrium is lost…
They Shrink a bit
And begin to fuse Hydrogen into Helium in a shell outside the core.

3. This Fusion generates more nuclear force than before.
Hydrostatic Equilibrium is lost again…
and they grow until they reach a new Hydrostatic equilibrium.
The heat is spread over a larger surface area
So it becomes cooler,
leaving the main sequence to become…
A Red Giant
Which it will be for 80 million years!

4. The Helium Flash Eventually the Core super-heats
Becoming hot enough to start fusing Helium into Carbon all of a sudden
The Helium Flash
This raises the temperature of the star and makes it a Yellow Giant.
But it is no longer stable
And moves into the “instability strip” with its size and luminosity changing
A Pulsating Yellow Giant
Which it will be for about 100 million years

5. The Sun becomes a Supergiant and dies
When the Sun like star starts to run out of helium its fusion slows and the core shrinks.
This briefly speeds up fusion
The Star expands… and cools
Becoming a Red Supergiant
for about 15 million years.
In the cool outer layers flakes of Carbon and Silicon form
They are blown away by photons from the Core taking the outer layers of gas with them forming a …

6. Planetary Nebula
So called because through a small telescope they look like a planet.
They have nothing to do with planets!
They spread out disappearing after about 10,000 years

7. The ‘Ant nebula”
The Ant nebula is a side view of a planetary nebula

8. The End of a Sun-like Star
The bare hot core of the star that is left behind
becomes a white dwarf that fades slowly into
a black dwarf