•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)
•
•