© Lloyd

Charles said: "This is why the void left by the formation of the star in the middle of the Keyhole Nebula in Figure 1 is linear instead of spherical."

Can you outline the linear void you're referring to? I assume you're talking about darker areas. I see some darker areas that are nearly black and some that are dark gray.

I just did a search on nebulae to look for other voids. I came to this statement (at space: clouds of interstellar dust & gas have blossomed in ngc ... www.scoopnest.com546 × 479Search by image): "#Space: the Snake #Nebula, dark absorption clouds create an apparent starless void"

Do you agree that the snake shape is the outline of absorption clouds? To me it looks like an actual void, although I don't see much star formation in it. Here's an image that shows a large area around the Snake Nebula:

There are several dark areas there, some filamentary. If those are all clouds, do you have an idea how they form in such shapes? And have you looked into what such clouds consist of? Carbon maybe?

Here's an interesting article about dark nebulae or absorption clouds: http://abyss.uoregon.edu/~js/glossary/dark_nebula.html