Inverted bubbles and donut bubbles

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Image from the Milky Way Project.

This is an “inverted bubble”. A bubble is a nebula that got its shape with the help of massive stars (see MWP about page).

An inverted bubble is a bubble where the Polycylic aromatic hyrocarbons (PAHs) did not get destroyed by the strong UV-radiation of the stars, like in normal bubbles. PAHs do radiate photons with wavelengths of 8 µm, here in green. This way the colour-pattern in inverted bubbles is “inverted” and the researchers at the Milky Way Project do think this is because the inverted bubble is formed by intermediate-massive stars.

donut

This is a special inverted bubble, we call it “donut bubble”. A donut bubble does have only a few massive stars that can clear the centre from PAHs.
In the centre of a donut bubble is often a little bit of heated and shocked dust (red part of the image; 24 µm).
Not all inverted bubbles are donut bubbles, but as I searched in the #invertedbubble hashtags I found a few of the donut bubbles.

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