•Strange
counterintuitive result:
–As
star radiates away thermal energy it actually heats up
(because
as it shrinks gravity supplies even more energy)
–
•Star
continues to shrink till it gets hot enough inside for fusion (rather than gravity) to balance
energy being radiated
away.
•
•Nuclear
thermostat
–If
fusion reactions took place in a “box” with fixed walls:
•Fusion
Þ more energy Þhigher T Þ more fusion (explosion)
•
–If
fusion reactions take place in sun with “soft gravity walls”:
•If
fusion rate is too high T tries to go up but star expands and actually ends up cooling off – slowing down
fusion. (steady rate)
•
•