The Crescent Nebula by Dietmar Hager and Immo Gerber
The Crescent Nebula by Dietmar Hager and Immo Gerber

Astronomy, Astrophotos

Hot Crescent Rolls… A Bubble?

16 Oct , 2009 by

[/caption]

The Crescent Nebula, also known as NGC 6888, is a very well renown and most intriguing object located in the constellation Cygnus in the northern hemisphere. At an apparent size of about 18 by 13 arc-minutes it is a very pale nebula. Even in a moderate amateur telescope you can’t quite see this one unless you have absolute dark skies (or narrow band filters) and a decent “light bucket”. So how do we get a chance to study it? Photographically, of course…

Spanning some 25 by 18 light years, gazing at NGC 6888 means we are looking 4700 years into the past, a past that renders a nebula fueled and excited by the blue star at the center. And not just any blue star – but a high mass super-giant star – one that depleted its fuel at “full speed”. Not only was it a super giant, but hot… in the class of “Wolf Rayet” stars (HD 192163). Now, after only a couple of million years the “stellar gas” is almost used up and the star is standing right before a significant change: a supernova candidate. Behold a star that vents its outer layers into space at terrific speed!

“Images are used to constrain models of the ionization structure of nebular features.” says Brian D. Moore (et al) of the Department of Physics and Astronomy, Arizona State University, “From these models, we infer physical conditions within features and estimate elemental abundances within the nebula. The results of our analysis, together with the degree of small-scale inhomogeneity apparent in the images, call into question the assumptions underlying traditional methodologies for interpretation of nebular spectroscopy. The thermal pressure of photoionized clumps is higher than the inferred internal pressure of the shocked stellar wind, implying that the current physical conditions have changed significantly over less than a few thousand years.”

While the central star sustains severe loss of mass, the gas is holding lots of oxygen and hydrogen… just before the individual big “bang” of the WR-star creating a “hot bubble” whose struture can’t quite be explained yet. “A detailed analysis of the H I distribution at low positive velocities allowed us to identify two different structures very probably related to the star and the ring nebula. From inside to outside they are: (1) an elliptical shell, 11.8×6.3 pc in size, that embraces the ring nebula (labeled inner shell); and (2) a distorted H I ring, 28 pc in diameter, also detected in IR emission (outer shell). The borders of the inner shell strikingly follows the brightest regions of NGC 6888, showing the sites where the interaction between the nebula and the surrounding gas occurs. A third structure, the external feature, is a broken arc detected at slightly higher velocities than the former shells.” says Christina Cappa (et al), “We propose a scenario in which the strong stellar wind of HD 192163, expanding in an inhomogeneous interstellar medium, blew the outer shell during the main sequence phase of the star. Later, the material ejected by the star during the LBV (or RSG) and WR phases created NGC 6888. This material encountered the innermost wall of the outer shell originating the inner shell. The association of the external feature with the star and the nebula is not clear.”

For a look inside, view the full size image!

Many thanks to Dietmar Hager and Immo Gerber of TAO-Observatory for sharing this incredible image!

By    
Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status. (Tammy passed away in early 2015... she will be missed)


Sort by:   newest | oldest | most voted
Stargazer-Observatory
Member
October 16, 2009 10:55 AM

Dear folks!

First off: Thanks Tammy for this intruiging article and more important thanks for picking our image!

I’d like to announce our new remote observatory TAO-Observatory (specific website is yet to come…)
operated together with my close friend Immo Gerber. We share equipment and enthusiasm for imaging the celestial wonders.
At TAO-obs you will find an “old friend” there: the 9″ TMB folded apo-refractor which has found new home in south of france…
please visit:
http://stargazer-observatory/TAO_01.html

cheers, Dietmar

Stargazer-Observatory
Member
October 16, 2009 11:05 AM
Jon Hanford
Member
Jon Hanford
October 16, 2009 1:12 PM

What a great image of this well known object by none other than Hager et al! Interesting to see the different ionization zones (the blue vs pink component of the nebula) and the tiny absorption nebula projected near the central Wolf-Rayet star. This area also reminds me of the recently discovered (by 2 groups of amateur astronomers) nearby planetary nebula PN G75.5+1.7 as reported here by UT (see the Quattrocchi and Helm page http://www.lostvalleyobservatory.com/review.nebula1/ for details & pix!).

Anaconda
Member
Anaconda
October 16, 2009 1:36 PM

It is a beautiful image.

I like the filaments that are clearly visible in the image and different plasma regions.

The pink and bue hues give the picture an appealing vitality.

Jon Hanford
Member
Jon Hanford
October 16, 2009 1:59 PM

According to the Stargazer Observatory page for the image about 70 hours of total exposure time ensued for this Hydrogen-alpha, LRGB color composite! Indeed much ionized gas( like hydrogen, oxygen, nitrogen and sulfur ) is visible as being ionized by direct irradiation from the WR star but also the ferocious stellar wind blasting away into space. Photo details can be found here: http://www.stargazer-observatory.com/6888-tao.html .

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
October 16, 2009 3:14 PM

Anaconda Said:

I like the filaments that are clearly visible in the image and different plasma regions.

In case you didn’t know, those regions are called NEBULA, however, not all of it is ionised. Ionisation does not usually mean plasma, but I suppose everything damn thing to you is plasma.

Frankly, from past experience, you could tell in space what is plasma and what is ordinary run-of-the-mill neutral matter.

Manu
Member
Manu
October 16, 2009 3:57 PM

@HSB Crumb:
Frankly, I wonder who’s trolling now. I don’t see a problem with Anaconda’s comment on this post.

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 16, 2009 4:54 PM
The WR star is throwing off material and lots of UV and X-ray radiation. So there are a lot of atomic transitions and ionizations going on in this material ejected in this stellar wind. This is a very tenuous gas of ionized and excited atoms however. Spectographic data is needed to identify atomic species, electron transitions and the extent of ionization. If you were placed in the middle of it you would largely see empty space. A good model for this is a flourescent lamp, but very large and tenuous. This is a type of nebula, no more mysterious than any other. It will be blasted by a supernova and replaced by a much more extensive nebula. LC
Ivan3man_At_Large
Member
Ivan3man_At_Large
October 16, 2009 9:13 PM

@ Hon. Salacious B. Crumb,

Those “Electric Universe” cranks see plasma in every nebula like fundamentalist Christians see Jebus in every water/oil stain or cheese-on-toast! roll

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
October 16, 2009 9:30 PM

@ Anaconda

Here is two very good questions for you…

Are commonplace Hydrogen-Alpha ions seen in gaseous nebulae really plasma?

Also have you ever wonder why gaseous nebulae are NOT actually called plasma nebulae or even magnetic nebulae?

Pvt.Pantzov
Member
October 17, 2009 1:29 AM

attn admins:

please put a stop to this.

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
October 17, 2009 2:14 AM
Pvt.Pantzov Says: October 17th, 2009 at 1:29 am attn admins: please put a stop to this. I would suggest otherwise. It is about time the EU proponent and fringe elements be show up for the misinformation and deceptions. Why is it, that ordinary discussion has ti be hijacked by some lunatics who think all forums are cannon fodder for their wacky ideas and total irrelevancies? I like many here have worked in the sciences making a career involving investigation and study. Why should the respectable pillars of astronomy and associated subject be bulldozed by a bunch of misfits who think it their personal duty to undermine science for the sake of notoriety? Anoconda has inflicted misery just for… Read more »
Lawrence B. Crowell
Member
Lawrence B. Crowell
October 17, 2009 5:09 AM

Anaconda’s statements here are fairly innocuous. He is serving more of an anti-intellectual role on the blog site on the Multi-verse. Salacious B. Crumb might want to hammer him down over there. Of course the existence of ionized nebular gas is a perfect way for him to segue discussions into EU nonsense.

LC

Anaconda
Member
Anaconda
October 17, 2009 9:50 AM

“ionized gas” is plasma.

“Zone” is a region. Nebula refers to the object as a whole.

Filaments are evident in the image.

SBC, “personal duty to undermine science”, no, not at all.

I suggest considering all the possibilities actually bolsters the Scientific Method and furthers the purposes of science.

Why the hostility from some of the other commenters regarding an innocuous comment?

chairflyer2002
Member
chairflyer2002
October 17, 2009 12:03 PM
I’ll only make 1 comment on the war of the words being waged here. It could be, that Anaconda does not have the scientific knowledge to call the different forms of the OBJECT but Salacious,s “corrent termonology”. So Salacious should, in my opinion, LAY OFF of Anaconda, and anyone else who comments. NOW TO a couple things I wanted to post. Here again, I am not as knowledgable APPARENTLY as salacious, so whether some of the terminology ere hasalready brouth these up, is left to you other readers. Has anyone looked closely at the enlarged version of the photo, and seen the DARK hole area just left of the blue progenitor star? 2ndly, hass anyone noticed the concentric… Read more »
chairflyer2002
Member
chairflyer2002
October 17, 2009 12:06 PM

p.s. sorry for the typos

Ivan3man_At_Large
Member
Ivan3man_At_Large
October 17, 2009 1:29 PM

@ chairflyer2002,

Obviously, you are not familiar with Anaconda’s past “Electric Universe” rantings here and on Bad Astronomy, are you?

Ivan3man_At_Large
Member
Ivan3man_At_Large
October 17, 2009 2:35 PM

Oh, I just noticed… in the article above, at the fourth paragraph, in the first line, there’s a missing “c” in structure.

Ivan3man_At_Large
Member
Ivan3man_At_Large
October 17, 2009 2:39 PM

Correction: third line, not “first”.

*Grumble* No bloody edit facility here! *Grumble*

Mr. Man
Member
Mr. Man
October 17, 2009 2:40 PM

There was nothing wrong with Anaconda’s first comment, why are people getting all pissed off? Its entertaining to read everyone’s rant, but still…why?

wpDiscuz