- It looks like Hydrogen fusion will work as the power
source of the Sun. We have lots of the right fuel, the
conditions in the inner 10% of the Sun are right for the P-P
cycle to run, and it is a very efficient source of energy.
- Exactly how does the energy get from proton mass into
visible light photons flying from the surface of the Sun into
- -rays are released during the P-P fusion chain
and almost immediately (after traveling on average 1cm)
absorbed and re-emitted. The energy contained in that original
-ray bounces its way outward and after ~100,000
years and absorptions and re-emissions it leaves
the surface of the Sun ``downgraded'' into visible light
photons (because of the temperature gradient in the Sun).
- An interesting Aside: The Sun must be losing mass
as it is converted into energy.
- How Much?
This comes to
- One more fact and we can understand the Main Sequence
in the H-R Diagram (!)
- A more massive star has a higher or lower
central temperature? Higher of course - hydrostatic
equilibrium demands this.
- Higher central temperature means P-P rate is higher and
more energy is released - this means a larger luminosity.
- Pay attention now:
- So, this explains why there is a Luminosity-Temp
relation and why as you move to higher Temp and Luminosity along
the main sequence, you are moving along a mass sequence.
Fri Feb 6 23:24:56 PST 1998