The Helium Flash


On the Red Giant Branch, the core of the Sun is being compressed to higher densities and temperatures, but it takes a temperature of 100 Million Kelvins to ignite Helium fusion.

Before the temperature gets that high, something strange happens...


Thermal pressure is due to the random motions of particles at a given temperature. Higher temperature means faster random motions and higher pressures.


Pressure can also be generated by trying to pack particles in close together.

Q: How close can you pack electrons?

A: Heisenberg Uncertainty Principle


Electron Degeneracy

If pressure is supplied by electron degeneracy, it does not depend on temperature.

What happens when thermonuclear fusion begins in a stellar core supported by electron degeneracy?






The Helium Flash

For a few hours the fusion of helium into carbon in the core will produce a luminosity of 10 billion suns!

This energy is trapped in the core of the star, and the high pressure expands the core (but the envelope shrinks) until a stable burning is reached.

Life continues on the horizontal branch: a helium main sequence.

How long will the Sun burn Helium in the core?