What is the primary difference between the central energy source ionizing a PN versus an emission-type Diffuse Nebula?

Answer

PNs are ionized by the extreme UV flux of a hot, compact White Dwarf; Diffuse Nebulae are ionized by massive, young stars.

The compact, ultra-hot remnant of a low-mass star powers the PN, whereas the diffuse nebula is powered by the massive, luminous, newly formed stars within it.

What is the primary difference between the central energy source ionizing a PN versus an emission-type Diffuse Nebula?

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