How dense are the brightest regions of planetary nebulae?

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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.

The density of planetary nebulae varies throughout their evolution. In their dense regions, these nebulae typically contain between 1,000 and 10,000 atoms per cubic centimeter.1

During the earlier stages of their evolution, before the entire mass of the gas has become ionized, the gas can reach a relatively high density of approximately one million atoms per cubic centimeter. As the nebula continues to expand, this density decreases, becoming more dilute over time.2