De Marco, Orsola Department of Physics and Astronomy, Macquarie University, North Ryde, Sydney, New South Wales, Australia.
- Number of nebulae
- Appearance and images
- Chemical recycling
- Origin of shapes
- Future of the Sun
- Unanswered questions
- Related Primary Literature
- Additional Reading
The ejected outer layers of stars born with mass between approximately 1 and 8 times the solar mass. Toward the end of their lives, such stars go through the asymptotic giant branch phase. At the end of this phase they suffer a dramatic increase in mass loss rate, which reduces the star to its bare core. By then these stars have grown to a few hundred times the radius they had at the start of their lives and have lost some to most of their mass as they become white dwarf stars. The material that is lost during this phase slowly expands outward until the inner stellar core is hot enough to ionize it. The ionization fires up the ejected gas, which shines as a visible planetary nebula. These nebulae have various symmetric and usually striking shapes (Fig. 1). See also: Stellar evolution
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