APOD: Portrait of the Eagle Nebula (2022 Aug 12)

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APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by APOD Robot » Fri Aug 12, 2022 4:05 am

Image Portrait of the Eagle Nebula

Explanation: A star cluster around 2 million years young surrounded by natal clouds of dust and glowing gas, Messier 16 (M16) is also known as The Eagle Nebula. This beautifully detailed image of the region adopts the colorful Hubble palette and includes cosmic sculptures made famous in Hubble Space Telescope close-ups of the starforming complex. Described as elephant trunks or Pillars of Creation, dense, dusty columns rising near the center are light-years in length but are gravitationally contracting to form stars. Energetic radiation from the cluster stars erodes material near the tips, eventually exposing the embedded new stars. Extending from the ridge of bright emission left of center is another dusty starforming column known as the Fairy of Eagle Nebula. M16 lies about 7,000 light-years away, an easy target for binoculars or small telescopes in a nebula rich part of the sky toward the split constellation Serpens Cauda (the tail of the snake). As framed, this telescopic portrait of the Eagle Nebula is about 70 light-years across.

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by heehaw » Fri Aug 12, 2022 10:51 am

Exceptionally beautiful!

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by geoffrey.landis » Fri Aug 12, 2022 1:24 pm

the interesting illusion about today's Astronomy Picture of the Day of the Eagle Nebula is that our brains see the blue as a hole in the dark clouds showing sky behind.
But the sky in space is black, not blue. The blue is also a cloud, at about the same distance at the others.

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by orin stepanek » Fri Aug 12, 2022 2:50 pm

M16_final.jpg
Beautiful Eagle Nebula; so many figures made out in the Eagle! 8-)
M16_final_1024.jpg
My conception of a head in Eagle Nebula
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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by MarkBour » Fri Aug 12, 2022 4:19 pm

There's lots to wonder about in this beautiful image.
  1. To the upper left of the blue patch, is a red and milky white shape that looks like a solar prominence, or a two-thirds of a doughnut. It must be at least 5 light years in diameter. As I look at it, I think it is actually spherical, and the only reason it looks more like a doughnut is because front and center of it is a region of black-appearing dust that obscures the visually central part of it. So, what is it? Is it a planetary nebula? If so, it must have been a massive supernova, right?
  2. The blue patch, if this is the Hubble palette, must be a lot of oxygen. What could cause an abundance of oxygen in one region of the nebula?
  3. One can see what appear to be ripples, as if in a pond, all over the image, but most clearly to the lower right of the oxygen patch. I don't think these ripples appear to be centered on the first item in this list, they probably came from some other source. But I'm wondering if the ripples are remnants of a set of shocks that passed through the region of the Pillars of Creation and the Fairy, and set off the star formation that is progressing within them.
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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by bystander » Fri Aug 12, 2022 5:00 pm

geoffrey.landis wrote: Fri Aug 12, 2022 1:24 pm the interesting illusion about today's Astronomy Picture of the Day of the Eagle Nebula is that our brains see the blue as a hole in the dark clouds showing sky behind.
But the sky in space is black, not blue. The blue is also a cloud, at about the same distance at the others.
I see the image as the top left being furthest from us and the image flows out of the page to the lower right. The head of the eagle is furthest, while the back, wings, and tail are progressively closer. That's probably wrong, but that's just the way my eyes see it.
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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by Ann » Fri Aug 12, 2022 6:34 pm

geoffrey.landis wrote: Fri Aug 12, 2022 1:24 pm the interesting illusion about today's Astronomy Picture of the Day of the Eagle Nebula is that our brains see the blue as a hole in the dark clouds showing sky behind.
But the sky in space is black, not blue. The blue is also a cloud, at about the same distance at the others.
Well, there is kind of a hole in the Eagle Nebula.

M16_final_1024[1].jpg
Portrait of the Eagle Nebula
Image Credit & Copyright: Charles Bonafilia

Take a look at the Rosette Nebula in the picture at right. The way I understand it, the Rosette Nebula is a little older than the Eagle Nebula. According to Wikipedia, the cluster that ionizes the Eagle Nebula is 1-2 million years old, and I believe that the cluster ionizing the Rosette Nebula is just a little bit older, less than 5 million years old.

Here's my point. You can really see that there is a hole at the center of the Rosette Nebula. The hole has been blown by the massive stars at the center of the nebula. The Eagle Nebula is a little younger, so the cluster has not yet had time to blow such a perfect hole in the gas around itself, but clearly the gas has been attenuated.

So there is sort of a hole at the center of the the Eagle Nebula, even if there is still gas there. This gas is highly ionized, and the APOD makes it look blue from (really greenish cyan) OIII emission close to the extremely hot stars.

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by Ann » Fri Aug 12, 2022 6:41 pm

orin stepanek wrote: Fri Aug 12, 2022 2:50 pm Beautiful Eagle Nebula; so many figures made out in the Eagle! 8-) My conception of a head in Eagle Nebula
Love your Eagle Nebula head, Orin! :D

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by johnnydeep » Fri Aug 12, 2022 8:50 pm

geoffrey.landis wrote: Fri Aug 12, 2022 1:24 pm the interesting illusion about today's Astronomy Picture of the Day of the Eagle Nebula is that our brains see the blue as a hole in the dark clouds showing sky behind.
But the sky in space is black, not blue. The blue is also a cloud, at about the same distance at the others.
What a poetic observation!
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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by johnnydeep » Fri Aug 12, 2022 8:52 pm

Ann wrote: Fri Aug 12, 2022 6:41 pm ...
Love your Eagle Nebula head, Orin! :D

Ann
And it even looks like it's sleeping - note the dark line of a closed eyelid.
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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by johnnydeep » Fri Aug 12, 2022 8:57 pm

Pretty remarkable image. Looks almost like Hubble took it! It's amazing to me that this was taken with a "mere" Sky-Watcher Esprit 120ED.
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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by MarkBour » Sat Aug 13, 2022 8:39 am

geoffrey.landis wrote: Fri Aug 12, 2022 1:24 pm the interesting illusion about today's Astronomy Picture of the Day of the Eagle Nebula is that our brains see the blue as a hole in the dark clouds showing sky behind.
But the sky in space is black, not blue. The blue is also a cloud, at about the same distance at the others.
Indeed, even though it is false colors, that region looks very inviting.
Maybe the Universe is signaling to us:
"If you come here, you might find some habitable planets, with blue skies."
Mark Goldfain

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by johnnydeep » Sat Aug 13, 2022 12:14 pm

MarkBour wrote: Sat Aug 13, 2022 8:39 am
geoffrey.landis wrote: Fri Aug 12, 2022 1:24 pm the interesting illusion about today's Astronomy Picture of the Day of the Eagle Nebula is that our brains see the blue as a hole in the dark clouds showing sky behind.
But the sky in space is black, not blue. The blue is also a cloud, at about the same distance at the others.
Indeed, even though it is false colors, that region looks very inviting.
Maybe the Universe is signaling to us:
"If you come here, you might find some habitable planets, with blue skies."
I hereby dub it The Blue Lagoon in The Eagle Nebula! Stop on by - the waters are warm and inviting!
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"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by starsurfer » Sun Aug 14, 2022 10:23 pm

This image looks so much better north up!

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by Ann » Mon Aug 15, 2022 6:39 am

MarkBour wrote: Fri Aug 12, 2022 4:19 pm There's lots to wonder about in this beautiful image.
  1. To the upper left of the blue patch, is a red and milky white shape that looks like a solar prominence, or a two-thirds of a doughnut. It must be at least 5 light years in diameter. As I look at it, I think it is actually spherical, and the only reason it looks more like a doughnut is because front and center of it is a region of black-appearing dust that obscures the visually central part of it. So, what is it? Is it a planetary nebula? If so, it must have been a massive supernova, right?
  2. The blue patch, if this is the Hubble palette, must be a lot of oxygen. What could cause an abundance of oxygen in one region of the nebula?
  3. One can see what appear to be ripples, as if in a pond, all over the image, but most clearly to the lower right of the oxygen patch. I don't think these ripples appear to be centered on the first item in this list, they probably came from some other source. But I'm wondering if the ripples are remnants of a set of shocks that passed through the region of the Pillars of Creation and the Fairy, and set off the star formation that is progressing within them.

I'll belatedly try to answer some of your questions. I'll try, mind you! First, the two-thirds of a doughnut.

APOD 12 August 2022 M16 Charles Bonafilia.png

The semicircle of a half a doughnut is seen at upper left. It's definitely not a planetary nebula. To me, it is slightly - slightly, not very - reminiscent of the Flame Nebula:


The similarity between the "half a doughnut" and the Flame Nebula is that they are both found near hot stars, in an environment full of gas and dust, where there has recently been massive star formation going on. formation. The Flame Nebula is a site of star formation.

The huge difference between the Flame Nebula and the semicircle nebula in the Eagle Nebula is that the semicircle is so perfectly regularly formed, whereas the dark dust pillar in front of the Flame Nebula is very tattered and torn. And the upper edges of the Flame Nebula are very diffuse. My guess is that the stubby dust pillar in M16 is more of a foreground object and located quite some distance away from any actual star formation. It is sort of a counterpart to the large triangular kind of semi-transparent pillar hanging down from the "roof" of M16.

But could the semicircular shape have been caused by a supernova? It wouldn't be incredibly surprising to find a supernova here, close to such massive stars. But I don't think it looks like a supernova remnant. Let's look at NGC 604 in M33 and a supernova remnant in the the Small Magellanic Cloud:

In the wake of Independence Day festivities surrounding the U.S. July 4th holiday, astronomers and image processors at the Space Telescope Science Institute are releasing the Hubble Space Telescope image of a cosmic explosion that is quite similar to fireworks on Earth. In the nearby galaxy, the Small Magellanic Cloud, a massive star has exploded as a supernova, and begun to dissipate its interior into a spectacular display of colorful filaments. The supernova remnant (SNR), known as 'E0102' for short, is the greenish-blue shell of debris just below the center of the Hubble image. Its name is derived from its cataloged placement (or coordinates) in the celestial sphere. More formally known as 1E0102.2-7219, it is located almost 50 light-years (15 parsecs) away from of the edge of the massive star-forming region, N 76, also known as Henize 1956 in the Small Magellanic Cloud. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA).


In the image at left, we see the bisected NGC 604 in M33, where "the left lobe" is filled with X-rays from past supernovas, whereas the right lobe is filled with X-rays from stellar winds from massive young stars. In the image at right, the supernova remnant (blue and green) is separate from the region of star formation (pink).

I don't think that the semicircle is a supernova remnant. I expect a supernova remnant to "define its own shape", but the semicircle looks like it is defined by foreground dust hanging in front of some kind of "shapeless" ionized background.

Lets take a look at ESO:s BVR "natural-color" portrait of the Eagle Nebula:


In ESO's image, we can see that the ionization level of the semicircle (at upper right) is quite low. It is so low, in fact, that I'd say that it is impossible that any sort of massive star formation is going on behind the stubby dark dust pillar. Instead, I think that the semicircle is simply a (very interestingly shaped) break in the dust cloud cover, revealing scattered rather low-energy ionization from the massive young star cluster ionizing Eagle Nebula itself.


So, on to the blue center of the Eagle Nebula. I think that the first thing we must remember is that the APOD is a narrowband image, so that the emission from a single narrow wavelength can be incredibly dominant in such an image, even if such an image doesn't correspond to that wavelength's actual dominance in the area in question.


A great illustration can be seen here from Fort Lewis Observatory. There is a "hover image" alternating between an RGB+H-alpha and a Hubble palette image. This is what the two images look like:


As you can see, there is a lot of blue from OIII in the Hubble palette image, but there is no blue at all in the RGB+Hα image, where OIII was not specifically recorded. My point is that there is not and abundance of OIII in the blue-looking part of the Eagle Nebula, but there is really some OIII there.


Let's compare it with the ESO "naturl-color" image again:


The part of the Eagle Nebula near the young star cluster is "pale" in color. The overall hue of the nebula bleeds from red at the edges to pink to bluish white at the center. The bluish color is a combination of OIII and scattered light from the hot blue stars themselves, I'd say.

OIII emission is seen in rarefied regions near extremely hot stars, where there is very little gas and enormous amounts of ultraviolet photons. We do see some OIII in nebulas surrounding very hot young stars, such as the Eagle Nebula and the Orion Nebula.But the only place where OIII is dominant to the point that we can actually see the color of it in ordinary RGB images is in planetary nebulas (and not even in all planetary nebulas, but in most of them):


The green color in planetary nebula IC 1295 is "true". This nebula has got no (or extremely little) hydrogen, and virtually all the light from the nebula is the green light of OIII. The OIII is quite bright here.


So, in short: The very blue part of the Eagle Nebula seen in the APOD is so blue because of the choice of filters used for the image, and also because of choices made during processing.

Compare these two images of the Rosette Nebula:


Why is there so much blue in one of the Rosette Nebula images, and hardly any blue at all in the other one? It's because of the filters used and the choices made during processing.

Ann
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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by Chris Peterson » Mon Aug 15, 2022 1:51 pm

Ann wrote: Mon Aug 15, 2022 6:39 am
MarkBour wrote: Fri Aug 12, 2022 4:19 pm There's lots to wonder about in this beautiful image.
  1. To the upper left of the blue patch, is a red and milky white shape that looks like a solar prominence, or a two-thirds of a doughnut. It must be at least 5 light years in diameter. As I look at it, I think it is actually spherical, and the only reason it looks more like a doughnut is because front and center of it is a region of black-appearing dust that obscures the visually central part of it. So, what is it? Is it a planetary nebula? If so, it must have been a massive supernova, right?
  2. The blue patch, if this is the Hubble palette, must be a lot of oxygen. What could cause an abundance of oxygen in one region of the nebula?
  3. One can see what appear to be ripples, as if in a pond, all over the image, but most clearly to the lower right of the oxygen patch. I don't think these ripples appear to be centered on the first item in this list, they probably came from some other source. But I'm wondering if the ripples are remnants of a set of shocks that passed through the region of the Pillars of Creation and the Fairy, and set off the star formation that is progressing within them.

Compare these two images of the Rosette Nebula:


Why is there so much blue in one of the Rosette Nebula images, and hardly any blue at all in the other one? It's because of the filters used and the choices made during processing.
This pair (and some of the others you posted) demonstrates very well why narrowband, false color palettes are used. The image on the left reveals so much more than the other one. Most emission nebulas, when imaged in RGB for "true color", fail to reveal most of what is really going on inside them. H-alpha is so bright compared to other emission lines that an RGB image of an emission nebula is effectively monochromatic, and the majority of emission nebulas are dominated by hydrogen.
Chris

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Re: APOD: Portrait of the Eagle Nebula (2022 Aug 12)

Post by MarkBour » Mon Aug 15, 2022 7:35 pm

Ann wrote: Mon Aug 15, 2022 6:39 am
I'll belatedly try to answer some of your questions. I'll try, mind you!
...
Ann
Thanks!
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