NGC 7008
PK 93+5.2

Cygnus

RA 21 00 33.1
DEC 54 32 32

Type: Planetary Nebula
Size: 86.0"

Magnitude: 12
Central Star Mag: 13.2

A favorite target of mine during the summer months, I'm actually a little surprised that not only NGC7008 hasn't been selected in the past as an OOTW but it hasn't even been discussed here at DeepSkyForum!

2800 light years distant towards the Swan, NGC 7008 was discovered by William Herschel in 1787. The Fetus Nebula, an alias given it by an amateur astronomer Eric Honeycutt in the 2001 summer edition of Amateur Astronomy Magazine, is not like your typical planetary. In fact, it's so atypical Herschel didn't recognize it as a PN cataloging it in the same category as the Lagoon! Its structure proved to be a catalyst for extensive study, some of which was derived from data collected by the Hubble Space Telescope. NGC7008 is unique in not only its overall shape, but its two separate shells. Where did these shells come from? Could its central star go through to two PN phases? Inquiring minds needed to know.

As best as I can find, there are 3 competing theories into how 7008 became the shape that it is.

1. It's possible that the inner shell is actually expanding faster than the outer shell and it's the overtaking of the outer shell by the inner that is creating its unique shape. To further exacerbate the complex structure, the shells may be interacting with the interstellar medium. Varying densities in the IM may be taking its toll on the shells.

2. The dual shells could have formed by different materials which may have originated by different sources. In other words, NGC7008 may have formed when a close binary system, both similar in age, "died" very close in time to one another. One star may have gone through the asymptotic giant branch (AGB) phase with the other experiencing the same fate not too long afterwards. http://adsabs.harvard.edu/abs/2006A%26A...452..523K

3. The third theory may be that the structure of the PN may have formed due to the dying stars expanding gas shell interacting with planetary material in orbit around the star. This to me was the most interesting. I started to think about this during my research of 7008 and thought to myself this may be the most plausible, especially since PN are typically older stars that may in fact have planetary systems. When I started digging more, I found this fantastic article from 2008 echoing my own thoughts. How cool! This theory would also explain why not all PN are symmetrical and some have the wild shapes that they do.

Some sources online will indicate that a knot, located approximately 20" to eh NW of the central star, is in fact a distinct planetary in and of itself. Unfortunately, it is not as it is nothing but a condensation within NGC7008 itself. http://adsabs.harvard.edu/abs/1983A%26AS...52..399S

NGC7008 is a fantastic object in the eyepiece. Accented with a beautiful gold/blue 18" double star on its southern edge, NGC7008 may be seen in nearly any telescope with sufficient skies. The Fetus Nebula may look as a small uniform glow in scopes around 6" while scopes in the 10"-12" range, observers have noted an oval or kidney been shape with some mottling. North of 20" aperture, 7008 really offers up some tantalizing views! In my 25", you can see exactly why it was give the common name it has. It really does look like its namesake. While observing this object, my mind wanders between two thoughts. One is the ending in 2001: A Space Odyssey. (Don't ask. I just do) And in the other, I tend to see a bright "ear" shape with a brighter region extending from the brighter northern region down to the SW and a darkening in the center on the eastern edge. It's this easterly darkening that likens itself to an "ear canal" to me helping me see a human ear. I also find UHC and OIII filters work best, though I have zero notes mentioning the use of my NPB filter, something I'll try next time I'm out.

So there is this week's OOTW. A great visual PN with some real mystery behind it. Next time you're out, give the 3rd theory above some thought. Imagine what it would be like to be standing on a planet when your parent star decides to give up the goods, provided your civilization survived that far along. Now think about the fact that our own solar system will experience the same fate, colliding and interacting with the expanding shell that was our sun. And who knows. Maybe our sun will be the progenitor of such a unique PN for other civilizations to observe and study.

And as always,

"Give it a go and let us know!
Good luck and great viewing!"

http://apod.nasa.gov/apod/ap080825.html

ngc7008_hagercollab_c800.jpg