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What role does the central star play in a planetary nebula?

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Planetary nebula Southern Ring Nebula as captured by the James Webb Space Telescope in the near-infrared (left) and the mid-infrared (right). The dimmer star at the center of this scene has been sending out rings of gas and dust for thousands of years in all directions. The Southern Ring Nebula is approximately 2,500 light-years away.

In a planetary nebula, the central star—often called the nucleus—plays a critical role as the engine that drives the nebula's visibility and evolution.1

Its primary functions include:

Ionization: The central star is extremely hot, typically ranging from 25,000 K to over 200,000 K. It emits intense ultraviolet radiation that ionizes the surrounding gas shell, causing it to glow and become visible.12
Evolutionary Marker: The star’s state provides a precise record of the nebula's development. As the star evolves, it undergoes significant changes in temperature, luminosity, and radius. By observing the nebula's brightness and the ionization states of elements like hydrogen and helium, astronomers can estimate the star's temperature and the time elapsed since the shell was ejected.3
Transition to White Dwarf: The central star represents the exposed, hot core of a former red giant. Over a relatively short period of about 10,000 years, it continues to contract and eventually cools to become a dense white dwarf star, marking the final stage of its life cycle.234