In terms of astronomical timescale, how long does a Planetary Nebula actively glow?

Answer

Extremely brief, perhaps only a few thousand years.

The expanding shell of a PN becomes too diffuse to be excited by the white dwarf in approximately 50,000 years, making it an astronomically brief phenomenon.

In terms of astronomical timescale, how long does a Planetary Nebula actively glow?

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The 5 Types of Nebulae | Star Gazers - YouTube

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