[arecibo (Miguel)]

Hi, all.

Good to see that my rather naïve question gave birth to a brain storm of far from naïve contributions.

I'm interested in almost everything Astrophysical, so you've given me enough food for thought for month or years to come.

I would like to summarize what I've learned in this thread: My question (I realize now) was one about morphology (and the underlying Physics, of course). Or, rather, two questions about morphology, with a third implicit.

When you see images of nebulae, you notice three kind of shapes:

Highly regular, in many planetary nebulae.

Highly irregular, like in M42, M78, IC1318, IC5146, NGC7000, The Cone Nebula region, M8, M20, etc (I mention ones that I've imaged or seen at a telescope).

And mildly regular, in supernova remnants (I've seen less of these).

So it was an easy jump (not really well founded) to associate shape with physical origin. I know that (bright) irregular nebulae are of two kinds (emission and/or reflection), and that some ENe and RNe can be rather regular in shape (The Rosette Nebula, for example).

Ok. So, the shape of PNe is more or less explained to (my) satisfaction. The "less" part is to account for new developments (and variations on the nebula formation process and "final" shape, not because I'm not satisfied). The general shape of emission and reflection nebulae does not need a general explanation.

And my observations of SN was too limited for allowing a general conclussion about their shapes.

Let's say that my quest is fulfilled. However, I'll read "con gusto" more contributions to the theme.