APOD: The Butterfly Nebula from Hubble (2017 Feb 08)

Comments and questions about the APOD on the main view screen.
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Re: APOD: The Butterfly Nebula from Hubble (2017 Feb 08)

Post by Ann » Thu Feb 09, 2017 11:28 pm

MarkBour wrote:I find this image truly sublime. The coloring and the detail of the flows are fantastic! It would make a great poster.

It is my assumption that the imaged clouds of the nebula are mainly composed of material ejected from the star. Or are they by chance, mostly material that was in space near the star that its explosive shock-wave is pushing?
They would certainly come from the star. After all, when a planetary nebula is formed, half a solar mass of material or (much) more is typically ejected into space by the star.

But when stars are born, they often form small jets that hit the surrounding material and form bow shocks.
Newborn star with jets and bow shock (Herbig-Haro object).
(NASA, ESA, and M. Livio and the Hubble 20th Anniversary Team)
Wikipedia wrote:

Herbig–Haro (HH) objects are small patches of nebulosity associated with newly born stars, and are formed when narrow jets of gas ejected by those stars collide with nearby clouds of gas and dust at speeds of several hundred kilometres per second. Herbig–Haro objects are ubiquitous in star-forming regions, and several are often seen around a single star, aligned with its rotational axis.
This version of the same object as the one I posted a picture of clearly labels the bow shock a Herbig-Haro object (HH means Herbig-Haro).

But the Butterfly Nebula has no obvious bow shock. So we see no signs of surrounding matter that exists independently of the star being compressed by jets or outflows from the hot central star.
The Pleiades. NASA/ESA/AURA/Caltech.
The reason why we would see bow shocks near young stars is that there is typically a lot of surrounding gas and dust in the regions where star formation takes place. Planetary nebulas, by contrast, are old objects, where nothing remains of the natal cloud where the star originally was born. So for us to see a bow shock around a planetary nebula, it would have to produce strong outflows as the same time as it accidentally wandered into cosmic cloud, à la the Pleiades. Is the large Merope Nebula (to the lower right) something resembling a bow shock?

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