Stars as Laboratories for Fundamental Physics - MPP Theory Group

36 Chapter 2
Fig. 2.7. Ring Nebula in Lyra (M57), a planetary nebula. (Image courtesy
of Palomar/Caltech.)
For stars which start out sufficiently large the mass loss on the
AGB can be so dramatic that one may speak of the ejection of the
entire envelope. It forms a large shell of gas which is illuminated by
its central star, the newborn white dwarf. Such systems are known as
“planetary nebulae” (Fig. 2.7).
2.1.6 Type I Supernovae
A white dwarf can make a spectacular reappearance if it is in a binary
system. If the other member expands because it is in an earlier evolutionary
phase it can transfer mass, allowing for renewed nuclear burning
on the white-dwarf surface. This adds mass to the CO configuration
which ultimately becomes so hot and dense that these elements ignite,
leading to a (subsonic) deflagration or (supersonic) detonation front
which sweeps through the star and disrupts it entirely. This course of
events is the standard scenario for type I supernova explosions which
are among the most energetic events known in the universe. They must
be carefully distinguished from type II supernovae which are related to
the collapse of evolved, massive stars.