Planetary Nebula Formation. After the ejection of the envelope (slow stellar wind, red arrows) of the AGB (red giant, Asymptotic Giant Branch) star (through thermal pulsing or some other mechanism), the bare core of the AGB star (hot white dwarf, center) is revealed. The temperature of the core is over 100,000 Kelvins initially and is an intense source of Ultraviolet radiation and a high-speed stream of particles (fast stellar wind, light blue arrows).

• Fast wind moves away from the star at speeds of up to several thousand kilometers per second and easily overtake the ejected envelope of the AGB star. Fast wind compresses the ejected envelope of the star into a thin dense shell (cyan)
• The UV radiation strongly ionizes the gas in the shell, ionized shell emits visible light