APOD: IC 5146: The Cocoon Nebula (2022 Aug 27)

[APOD Robot]

IC 5146: The Cocoon Nebula

Explanation: Inside the Cocoon Nebula is a newly developing cluster of stars. Cataloged as IC 5146, the beautiful nebula is nearly 15 light-years wide. Climbing high in northern summer night skies, it's located some 4,000 light years away toward the constellation Cygnus the Swan. Like other star forming regions, it stands out in red, glowing, hydrogen gas excited by young, hot stars, and dust-reflected starlight at the edge of an otherwise invisible molecular cloud. In fact, the bright star found near the center of this nebula is likely only a few hundred thousand years old, powering the nebular glow as it clears out a cavity in the molecular cloud's star forming dust and gas. A 29 hour long integration with a small telescope from Ayr, Ontario, Canada resulted in this exceptionally deep color view tracing tantalizing features within and surrounding the dusty stellar nursery.

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[Ann]

Red emission nebula IC 5146, the Cocoon Nebula, and blue reflection nebula vdB 147. Image Credit & Copyright: David Jenkins

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The Cocoon Nebula. Photo: Marcel Drechsler.

The Cocoon Nebula widefield. Photo: Tommy Knutsen.

Today's APOD looks fine, but I think we need to take a more widefield approach to understand more about the nature of this nebula. Marcel Drechsler's image (top right) shows colorful nebulosity surrounding the rosy red emission nebula of IC 5146 proper. A bluish reflection nebulosity can be seen encircling the central red emission nebula, and two deep red "wings" of emission nebulosity protrude from the main body, giving the nebula the appearance of a bird. Or perhaps it is more like an airplane, because we can see a long thick "exhaust trail" of dusty gas flowing from the nebula toward the lower left.

Tommy Knutsen's image "puts the Cocoon Nebula in its place" some distance away from the North America Nebula and Deneb. We can see how small the Cocoon Nebula is, although appearances are somewhat deceiving: The way I understand it, the Cocoon Nebula is twice as far away from us as the North America Nebula. Note that the tiny Cocoon Nebula is located at the tip of a long dark dust lane.

But the Cocoon Nebula is small. It is powered by a single hot star, and this star isn't even an O-type star. We are talking about B1V-type BD+46 3474 or TYC 3608-1446-1. The star is too faint in our skies to even have an HD or an SAO designation. According to Wikipedia, the size if the Cocoon Nebula is about 15 light-years, and the age of the ionizing star is only about 100,000 years.


I was struck by how much the Cocoon Nebula really resembles the Trifid Nebula:

The Cocoon Nebula. Photo: Adam Block/Mount Lemmon SkyCenter/University of Arizona.

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The Trifid Nebula. Nova Dawn Astrophotography.

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Both the Cocoon Nebula and the Trifid Nebula have round red emission centers, ionized by a single star or a very small group of stars. Both nebulas and their ionizing stars are very young. Both nebulas display prominent dust lanes crisscrossing the red emission center. Both nebulas are surrounded by a bluish reflection nebulosity.

I googled "Trifid Nebula wiki" to see how big the Trifid Nebula is compared with the Cocoon Nebula, and to find out how old the ionizing central star of the Trifid Nebula is compared with BD+46 3474 of the Cocoon Nebula, which is apparently 100.000 years old.

Unfortunately, I could find no Wikipedia information on the age of the ionizing star of the Trifid, HD 164492A, which is however an O7.5III star, and thus much hotter than a B1V star. But the radius of the Trifid is said to be 21 light-years, compared with (the way I understand it) a 15 ly diameter for the Cocoon. So clearly the Trifid Nebula is both larger and brighter than the Cocoon.

They do look similar, nevertheless.

Ann

[AVAO]

Note that the tiny Cocoon Nebula is located at the tip of a long dark dust lane.

ThanX Ann, Great post!

One question: For me it looks like the dust lane is GENERATED BY the star as an "exhaust trail" and not the other way around, as is often argued. What is your opinion?

Jac

https://a4.pbase.com/o6/50/724550/1/101 ... 31280G.jpg
Copyright: Bob Starzynski (https://www.pbase.com/bobstarzynski/ima ... 9/original)

[daddyo]

29 hours is a long time to hold a camera still

[Ann]

Note that the tiny Cocoon Nebula is located at the tip of a long dark dust lane.

ThanX Ann, Great post!

One question: For me it looks like the dust lane is GENERATED BY the star as an "exhaust trail" and not the other way around, as is often argued. What is your opinion?

Jac

https://a4.pbase.com/o6/50/724550/1/101 ... 31280G.jpg
Copyright: Bob Starzynski (https://www.pbase.com/bobstarzynski/ima ... 9/original)

Interesting question, Jac. My opinion, or my guess, is that star formation may take place at the tip of long dust lanes, in the same way that star formation often takes place at the tip of dust pillars near hot stars. The reason for star formation at the tip of long dust lanes and at the tip of dust pillars would be the same: A column of dust meets resistance of some kind, a strong wind, an onslaught of ultraviolet photons, a shock wave etc, leading to the tip of the dust pillar getting compressed, and star formation taking place.

View of the IC 5146 star-forming region from ESA's Herschel Space Telescope. The Cocoon Nebula has formed at the tip of a Milky Way dust lane.

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Dust pillar with star formation in the Carina Nebula.
Photo: NASA, ESA, N. Smith and the Hubble Heritage Team.

Ann

[orin stepanek]

Nice photo!

[AVAO]

... Interesting question, Jac. My opinion, or my guess, is that star formation may take place at the tip of long dust lanes, in the same way that star formation often takes place at the tip of dust pillars near hot stars. The reason for star formation at the tip of long dust lanes and at the tip of dust pillars would be the same: A column of dust meets resistance of some kind, a strong wind, an onslaught of ultraviolet photons, a shock wave etc, leading to the tip of the dust pillar getting compressed, and star formation taking place. ...

Ann

ThanX Ann for your interesting input.
In my conception, older stars produce the molecular dust that is then needed in order to allow young stars to form again in condensed areas. a cosmic material flow cycle, so to speak. In any case, an exciting research topic for the JWST and IC 5146 a nice target in IR

Click to view full size image 1 or image 2

jac berne (flickr) Composit (Original data: NASA/ESA/JPL-Caltech/UCLA (HERSCHEL/WISE)

[Ann]

... Interesting question, Jac. My opinion, or my guess, is that star formation may take place at the tip of long dust lanes, in the same way that star formation often takes place at the tip of dust pillars near hot stars. The reason for star formation at the tip of long dust lanes and at the tip of dust pillars would be the same: A column of dust meets resistance of some kind, a strong wind, an onslaught of ultraviolet photons, a shock wave etc, leading to the tip of the dust pillar getting compressed, and star formation taking place. ...

Ann

ThanX Ann for your interesting input.
In my conception, older stars produce the molecular dust that is then needed in order to allow young stars to form again in condensed areas. a cosmic material flow cycle, so to speak. In any case, an exciting research topic for the JWST and IC 5146 a nice target in IR

Click to view full size image 1 or image 2

jac berne (flickr) Composit (Original data: NASA/ESA/JPL-Caltech/UCLA (HERSCHEL/WISE)

You are right, Jac. Interstellar dust is primarily created by aging stars. The dust that we see in star forming regions and in galactic dust lanes bears witness to the demise and death of previous generations of massive stars.

(And just so that Chris will not pop in here and correct me: Yes, I know that those dark dust lanes and dust pillars are primarily made of gas, and it is the gas that is compressed so that it forms new stars. It is just that the gas is invisible, but we can see the dust.)

I'm just saying that I think that the tip of dark columns is a particularly favorable place for stars to form, if the material at the tip of the column of gas and dust is compressed.

Ann

[AVAO]

Last edited by bystander on Sat Aug 27, 2022 2:50 pm, edited 1 time in total.
Reason: Please, no hot links to images > 500 kb. Substituted smaller image. (image 2)

Sorry and thanX to bystander for the immediate support. I'll remember it for the future

[MarkBour]

Nice discussion AVAO and Ann, and thanks for the context images. I wonder what led to the dark red airplane shape you pointed out in one of your posted images, Ann. Some of these natural questions would be easier to answer if we could observe for a few million years. Since we can't, deducing distant past from our view of the universe almost as a single still life image is a fun challenge that astronomy provides.

• "Which came first, the dust or the star?" or at least
• Did star X create dust structure Y?

I think in most cases, if you study the situation enough, answers to those questions would be able to be settled.
I'm not the expert, AVAO, but wouldn't this have to be a very violent, late-stage star, to be giving off appreciable dust before the end of its life? Like a Wolf-Rayet star, or Betelgeuse. But even a more well-behaved star, if sufficiently energetic, can do a lot to carve and shape dust that was there before it was born, if that's what you mean.

[johnnydeep]

Note that the tiny Cocoon Nebula is located at the tip of a long dark dust lane.

ThanX Ann, Great post!

One question: For me it looks like the dust lane is GENERATED BY the star as an "exhaust trail" and not the other way around, as is often argued. What is your opinion?

Jac

https://a4.pbase.com/o6/50/724550/1/101 ... 31280G.jpg
Copyright: Bob Starzynski (https://www.pbase.com/bobstarzynski/ima ... 9/original)

I'd say there's about a zero chance that a star (let alone a star that's part of the young cluster) generated that huge dust trail. I think it's too disordered and discontinuous. Just my uneducated feeling of course. Nevertheless, I'm reminded of the "puffer train" structures in "Conway's Game of Life", where simple starting patterns DO generate trails of debris:

[AVAO]

Nice discussion AVAO and Ann, and thanks for the context images. I wonder what led to the dark red airplane shape you pointed out in one of your posted images, Ann. Some of these natural questions would be easier to answer if we could observe for a few million years. Since we can't, deducing distant past from our view of the universe almost as a single still life image is a fun challenge that astronomy provides.

• "Which came first, the dust or the star?" or at least
• Did star X create dust structure Y?

I think in most cases, if you study the situation enough, answers to those questions would be able to be settled.
I'm not the expert, AVAO, but wouldn't this have to be a very violent, late-stage star, to be giving off appreciable dust before the end of its life? Like a Wolf-Rayet star, or Betelgeuse. But even a more well-behaved star, if sufficiently energetic, can do a lot to carve and shape dust that was there before it was born, if that's what you mean.

When I look at the first images from JWST, I only see stars with dust plumes, at least for those that are a little larger or closer.



https://live.staticflickr.com/65535/521 ... 295a_o.jpg
https://www.flickr.com/photos/194798982 ... otostream/