Death of small stars
In a low mass star in its last stage, with a helium burning shell, stellar modelling suggests that the helium burning shell becomes unstable, and
burns in bursts. This causes the star to eject much of its outer layers.
The result is a ``planetary nebula'' which may last for 50,000 years before
it dissapates into space.
Here is some evidence. (Colors in general aren't exactly real in these
Left behind in the middle is a white dwarf star.
- The Egg Nebula,
where this process seems to be going on now. It appears that light gets
out near the poles of the star and is reflected from dust.
- NGC7027. The outer layers
appear to have been ejected in a spherically symmetric fashion; the inner
layers are more disorganized.
- MyCn18, The Hourglass Nebula
- NGC6543, the Cat's Eye Nebula,
a quite complex planetary nebula, possibly associated with a dying member of
a binary system.
Type Ia supernovae
There are observed very violent explosions called supernovae. It
appears that one kind of supernova is induced when extra mass from
a companion star falls onto a white dwarf. The carbon core gets
hot enough to begin fusion reactions, and does so explosively. It
is like a huge nuclear bomb.
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA