Death of a Low Mass Star (M = 0.4 to 8 Solar Mass) Important points include: Main Sequence, when the star is fusing H -> He at the core. Red Giant Branch when the core begins to collapse and the star is burning H -> He in shells outside the Helium rich core. The Helium Flash which may be sudden, like a flash, or a slower process, initiates He fusion into C at the core.

During the Horizontal Branch, the star is fusing He -> C in its core. As the core collapses further, the star fuses He -> C in outer shells, and moves once again up the HRD along the Asymptotic Giant Branch (AGB). As the low mass stars ascends the Asymptotic Giant Branch, it becomes enormously large. Our sun will engulf Mercury, Venus and perhaps even the Earth when it goes through this stage in 5 billion years.

The outer atmosphere (or envelope) continues to expand away, until the core becomes visible, making a Planetary Nebula. This bare core is what later will be known as a White Dwarf. Click HERE for an animation of a dying star. For a Mosaic of gorgeous nebula (not all are planetary) go here. Planetary nebulae are among the most beautiful objects in the sky. Below are links to PNe pretty-picture sites:

• Hubble Space Telescope Gallery of Planetary Nebula Images

• Bruce Balick's Planetary Nebula Gallery at SEDs.

• George Jacoby's Planetary Nebula Sampler at NOAO.