Starship Asterisk*

Cocoon Nebula Wide Field

Explanation: When does a nebula look like a comet? In this crowded starfield, covering over two degrees within the high flying constellation of the Swan (Cygnus), the eye is drawn to the Cocoon Nebula. A compact star forming region, the cosmic Cocoon punctuates a nebula bright in emission and reflection on the left, with a long trail of interstellar dust clouds to the right, making the entire complex appear a bit like a comet. Cataloged as IC 5146, the central bright head of the nebula spans about 10 light years, while the dark dusty tail spans nearly 100 light years. Both are located about 2,500 light years away. The bright star near the bright nebula's center, likely only a few hundred thousand years old, supplies power to the nebular glow as it helps clear out a cavity in the molecular cloud's star forming dust and gas. The long dusty filaments of the tail, although dark in this visible light image, are themselves hiding stars in the process of formation, stars that can be seen at infrared wavelengths.

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This is an interesting APOD. I assume that the red background is hydrogen alpha, brought out by an Hα filter.

Obviously the fascinating aspect of this APOD is how it shows us a long tendril of dust (actually, it is mostly gas, mixed with dust), which ends in a region of star formation.

This is not unheard of. Gas and dust very often form elongated dark structures in the Milky Way, perhaps because of our galaxy's rotation. Or has it something to do with magnetic field lines?

Star formation is by no means rampant in the Milky Way, and many, many dust structures are "sterile". But some long dust lanes do form stars at one end:




And what is the Antares and Rho Ophiuchi region, if not (massive) star formation at the end of a long dust lane? Another long dust lane has ended in the Blue Horse region and the "claws" of Scorpius (or whatever Beta, Delta, Pi and maybe Rho Scorpius are collectively called).


Scorpius is the constellation where we find Antares, but it is also home of the False Comet. And the "comet head" of the False Comet, the hot stars of NGC 6231, is in the process of compressing gas in a nearby cometary globule, an elongated dust structure with star formation at the end closest to the bright cluster. The cometary globule in question is known as the Dark Tower.


In the cometary globule known as the Dark Tower, we can see how harsh ultraviolet radiation and stellar winds from massive cluster NGC 6231 have sculpted and compressed a thick strand of gas and made it form stars at the end closest to the brilliant cluster. Maybe something at least slightly similar has happened in other places where stars have formed at one end of a long dust lane.

Ann

Comet Cocoon! I like this nebula with the tail! Does this show a direction that the
Cocoon is moving? Dog is watching!

orin stepanek wrote: ↑Wed Oct 26, 2022 2:32 pm
....Does this show a direction that the Cocoon is moving?

Very good question, Orin! Comparing with the 2002 APOD (2002 October 14) photo we can see that smaller stars are primarily moving along the two main filaments (dark outflow streams towards 11 and 5 o'clock on todays APOD) of the central star (BD+46 3474). But the central star itself does not move noticeably. I assume that these two outflow streams flow into the two big dust tails (where the lower tail is partially interrupted), which point (or are pulled) towards the center of the galaxy. However, 20 years is probably too short a time difference to be able to determine a general movement of the star rosette "by eye". Gaia should actually make this possible. However, its data acquisition history is probably still too short. (By interest, there are currently 52 Arxiv papers about BD+46 3474 ) Jac


jac berne (flickr) https://live.staticflickr.com/65535/524 ... de71_o.jpg


The great explanation by Rob:

"The Cocoon Nebula IC 5146 (Distance 3900 light years) is a beautiful emission and reflection cloud that surrounds the illuminating central star BD +46°3474. The circular HII region is catalogued separately as Sharpless 125. The powerful B-type star, BD +46°3474 is the dominant illumination source of IC 5146 and lies in the foreground of a large molecular cloud complex. The colorful nebula IC 5146 is located at the eastern end of a series of dark clouds known as LDN 1035 and LDN 1045 (Lynds 1962) (also catalogued as Barnard 168). The central cluster of IC 5146 is a very young open cluster with a median age of about one million years. The cluster is so young that many of its members are still pre-main sequence stars. Among the young stars several young Herbig-Haro objects and many T-tauri objects are found. T-tauri stars are the pre-main sequence counterpart to low mass stars similar to our sun. They are detectable in h-alpha light as their dusty envelopes emit strongly in the shorter wavelengths. The bright star BD +46°3471, just west of the main IC 5146 illuminates a small reflection cloud lying near the western edge of the cloud complex. It is classified as a Herbig Be star. These stars are pre-main sequence intermediate mass stars (2 to 8 solar masses) which are often associated with dust or reflection nebulosity.

The cluster of stars which lie at the center of IC 5146 are mostly low mass stars like our sun but much younger at only 1 million years old. The nebula is powered by the hot and luminous B0 type star BD +46°3474 whose surface temperature of 30,000 to 35,000 degrees allows it to generate the ultraviolet flux needed to ionize the surrounding gases. The central star began to shine only one hundred thousand years ago along the near side of the current molecular cloud it illuminates.

The formation and evolutionary history of IC 5146 is suggested by its three dimensional structure. The mass tied up in the cluster members (64 solar masses) is much greater than the mass of the surrounding cloud (18 solar masses) suggesting that the young cluster likely formed in a foreground cloud that has since dissipated. Once formed, BD+46°3474 quickly evaporated the foreground cloud and went on to ionize a thin "blister" on the large background molecular cloud. Although BD +46°3474 is central within the bright nebulosity, the young T-tauri stars are asymmetrically distributed around the star suggesting they outline the boundary of the original cloud. Since that time the energetic winds of BD+46°3474 have carved out a cavity from the near side of the molecular cloud complex. Heated gas and dust flow like champagne from the molecular cloud, exiting the cavity in the direction of our sun where it is expelled. Fortuitously for astronomers the cavity has cleared a visual portal allowing direct observation of the innermost regions of the nebula and its cluster."

Robert Gendler http://www.robgendlerastropics.com/Cocoontext.html

Just like to mention that the dark nebula is catalogued as B168.

AVAO wrote: ↑Wed Oct 26, 2022 5:34 pm

orin stepanek wrote: ↑Wed Oct 26, 2022 2:32 pm
....Does this show a direction that the Cocoon is moving?

Very good question, Orin! Comparing with the 2002 APOD (2002 October 14) photo we can see that smaller stars are primarily moving along the two main filaments (dark outflow streams towards 11 and 5 o'clock on todays APOD) of the central star (BD+46 3474). But the central star itself does not move noticeably. I assume that these two outflow streams flow into the two big dust tails (where the lower tail is partially interrupted), which point (or are pulled) towards the center of the galaxy. However, 20 years is probably too short a time difference to be able to determine a general movement of the star rosette "by eye". Gaia should actually make this possible. However, its data acquisition history is probably still too short. (By interest, there are currently 52 Arxiv papers about BD+46 3474 ) Jac


jac berne (flickr) https://live.staticflickr.com/65535/524 ... de71_o.jpg


The great explanation by Rob:

"The Cocoon Nebula IC 5146 (Distance 3900 light years) is a beautiful emission and reflection cloud that surrounds the illuminating central star BD +46°3474. The circular HII region is catalogued separately as Sharpless 125. The powerful B-type star, BD +46°3474 is the dominant illumination source of IC 5146 and lies in the foreground of a large molecular cloud complex. The colorful nebula IC 5146 is located at the eastern end of a series of dark clouds known as LDN 1035 and LDN 1045 (Lynds 1962) (also catalogued as Barnard 168). The central cluster of IC 5146 is a very young open cluster with a median age of about one million years. The cluster is so young that many of its members are still pre-main sequence stars. Among the young stars several young Herbig-Haro objects and many T-tauri objects are found. T-tauri stars are the pre-main sequence counterpart to low mass stars similar to our sun. They are detectable in h-alpha light as their dusty envelopes emit strongly in the shorter wavelengths. The bright star BD +46°3471, just west of the main IC 5146 illuminates a small reflection cloud lying near the western edge of the cloud complex. It is classified as a Herbig Be star. These stars are pre-main sequence intermediate mass stars (2 to 8 solar masses) which are often associated with dust or reflection nebulosity.

The cluster of stars which lie at the center of IC 5146 are mostly low mass stars like our sun but much younger at only 1 million years old. The nebula is powered by the hot and luminous B0 type star BD +46°3474 whose surface temperature of 30,000 to 35,000 degrees allows it to generate the ultraviolet flux needed to ionize the surrounding gases. The central star began to shine only one hundred thousand years ago along the near side of the current molecular cloud it illuminates.

The formation and evolutionary history of IC 5146 is suggested by its three dimensional structure. The mass tied up in the cluster members (64 solar masses) is much greater than the mass of the surrounding cloud (18 solar masses) suggesting that the young cluster likely formed in a foreground cloud that has since dissipated. Once formed, BD+46°3474 quickly evaporated the foreground cloud and went on to ionize a thin "blister" on the large background molecular cloud. Although BD +46°3474 is central within the bright nebulosity, the young T-tauri stars are asymmetrically distributed around the star suggesting they outline the boundary of the original cloud. Since that time the energetic winds of BD+46°3474 have carved out a cavity from the near side of the molecular cloud complex. Heated gas and dust flow like champagne from the molecular cloud, exiting the cavity in the direction of our sun where it is expelled. Fortuitously for astronomers the cavity has cleared a visual portal allowing direct observation of the innermost regions of the nebula and its cluster."

Robert Gendler http://www.robgendlerastropics.com/Cocoontext.html

That's a very fascinating piece of information, and I find it particularly intriguing that the young T Tauri stars are asymmetrically distributed around the bright central star in a way that suggests the outline of the original cloud.

But I think that Rob Gendler is exaggerating the properties of BD+46°3474. According to both Simbad and other sources I have seen, this star is spectral class B1. As such, its temperature could be 30,000 K (I guess), but not 35,000 K. A star of spectral class B1 is not that hot.

Wikipedia wrote:
The most-massive stars in the region is BD +46 3474, a star of class B1 that is an estimated 14±4 times the mass of the sun.

Ann