APOD: In the Heart of the Rosette Nebula (2023 Feb 06)

[APOD Robot]

In the Heart of the Rosette Nebula

Explanation: In the heart of the Rosette Nebula lies a bright cluster of stars that lights up the nebula. The stars of NGC 2244 formed from the surrounding gas only a few million years ago. The featured image taken in mid-January using multiple exposures and very specific colors of Sulfur (shaded red), Hydrogen (green), and Oxygen (blue), captures the central region in tremendous detail. A hot wind of particles streams away from the cluster stars and contributes to an already complex menagerie of gas and dust filaments while slowly evacuating the cluster center. The Rosette Nebula's center measures about 50 light-years across, lies about 5,200 light-years away, and is visible with binoculars towards the constellation of the Unicorn (Monoceros).

<< Previous APOD

This Day in APOD

Next APOD >>

[AVAO]

In the Heart of the Rosette Nebula

It really has that much oxygen (blue) here?
What's the source of this huge oxygen production?

APOD 2023 February 6

"The featured image ... using multiple exposures and very specific colors of Sulfur (shaded red), Hydrogen (green), and Oxygen (blue),.."
Image Credit & Copyright: Lyman Insley

APOD 2000 January 11

"Here green light originating from oxygen and blue light originating from sulfur supplements the red from hydrogen."
Credit: T. A. Rector, B. Wolpa, M. Hanna (AURA/NOAO/NSF)

APOD 2004 March 25

"In this image, sulfur is red, hydrogen is green, and oxygen is blue, a color scheme used in images of other astronomical nebulae as well."
Credit & Copyright: Russell Croman


"The Soul Nebula rendered in the Hubble color palette where sulfur, hydrogen and oxygen are color mapped to red, green and blue,..."
https://utahdesertremote.com/a-tale-of-two-color-palettes/

[Knight of Clear Skies]

It really has that much oxygen (blue) here?
What's the source of this huge oxygen production?

There are a couple possibilities I can think of here, hopefully someone more knowledgeable can shed more light on this.

The Rosette is an evolved star forming nebulae, stellar winds from the young bright stars at its core have carved out a central cavity. Oxygen has a higher molecular mass than hydrogen, so it may be expelled less easily leading to a relative concentration.

Oxygen also requires more energy to ionize than hydrogen, so the OIII signal may fall off more quickly with increasing distance from the ionizing sources.

[dddavids]

Does the pink color of the stars indicate that they are all rich in sulfur at the surface?

[Ann]

It really has that much oxygen (blue) here?
What's the source of this huge oxygen production?

There are a couple possibilities I can think of here, hopefully someone more knowledgeable can shed more light on this.

The Rosette is an evolved star forming nebulae, stellar winds from the young bright stars at its core have carved out a central cavity. Oxygen has a higher molecular mass than hydrogen, so it may be expelled less easily leading to a relative concentration.

Oxygen also requires more energy to ionize than hydrogen, so the OIII signal may fall off more quickly with increasing distance from the ionizing sources.

The NGC 2244 star cluster (whose most massive members ionize the Rosette Nebula and make it glow) is not evolved. The very fact that the stars of the NGC 2244 cluster are still surrounded by their birth cloud (i.e., they are surrounded by their own birth nebula) demonstrates that they are most likely not evolved. Indeed, Simbad Astronomical Database states that the most massive star, HD 46150, is still a main sequence star. According to Simbad, the spectral class of HD 46150 is O5V((f))z. The O5 means that this is not just an O-type star, but hotter than most O-type stars, and the "V" means main sequence. And the fact that HD 46150 is a main sequence star means that it is not evolved, and it is still fusing hydrogen to helium in its core. (But don't aske me about the ((f))z thing.)

And we have no special reason to believe that the Rosette Nebula is more oxygen-rich than most nebulas.

Ann

[orin stepanek]

Ah! The beautiful Rossette!

Foolish Puppy!

[Holger Nielsen]

Using Wikipedia and the SIMBAD database I have identified the following stars:
The brightest one in the picture is a foreground star, 12 Monocerotis, a K0 giant at a distance of 462 la with V = 5.83.
The bright blue star to its right is the O4 star HD 46223 at a distance of 4680 la with V = 7.28. The brightest pink star above this pair is HD 46150, an O5 star at 5072 la distance with V = 6.73.
The two O-stars are the brightest belonging to the cluster. In this picture their colors are quite different.

By the way, which of these would be correct:

• "a G2 star"
  "an O5 star"
  "a O5 star"

[Ann]

Using Wikipedia and the SIMBAD database I have identified the following stars:
The brightest one in the picture is a foreground star, 12 Monocerotis, a K0 giant at a distance of 462 la with V = 5.83.
The bright blue star to its right is the O4 star HD 46223 at a distance of 4680 la with V = 7.28. The brightest pink star above this pair is HD 46150, an O5 star at 5072 la distance with V = 6.73.
The two O-stars are the brightest belonging to the cluster. In this picture their colors are quite different.

By the way, which of these would be correct:

• "a G2 star"
  "an O5 star"
  "a O5 star"

You say (or I, a Swede, ) would say:

"a G2 star"
"an O5 star"

I would also say, "a B-type star", "an A-type star", "an F-type star", "a K-type star", "an M-type star" and "an L-type star".

That's because the letters F, M and L begin with a vowel sound when you pronounce them: "eff", "em" and "el". But K and G, apart from being consonants, begin with a consonant sound when you pronounce them: "/keɪ‎/‎" and "/dʒiː/.

The vowels A and O are pronounced with a vowel sound in the beginning. But other vowels, like U and Y, are pronounced with a consonant sound in the beginning. So if there were any U and Y stars, you would say "a U-type star" and "a Y-type star".

Ann

[Ann]

In the Heart of the Rosette Nebula

It really has that much oxygen (blue) here?
What's the source of this huge oxygen production?

APOD 2023 February 6

"The featured image ... using multiple exposures and very specific colors of Sulfur (shaded red), Hydrogen (green), and Oxygen (blue),.."
Image Credit & Copyright: Lyman Insley

APOD 2000 January 11

"Here green light originating from oxygen and blue light originating from sulfur supplements the red from hydrogen."
Credit: T. A. Rector, B. Wolpa, M. Hanna (AURA/NOAO/NSF)

APOD 2004 March 25

"In this image, sulfur is red, hydrogen is green, and oxygen is blue, a color scheme used in images of other astronomical nebulae as well."
Credit & Copyright: Russell Croman


"The Soul Nebula rendered in the Hubble color palette where sulfur, hydrogen and oxygen are color mapped to red, green and blue,..."
https://utahdesertremote.com/a-tale-of-two-color-palettes/

Today's APOD is a mapped color image. While the APOD shows us structures in the Rosette Nebula that are really there, it would be a big mistake to use a mapped color image to try to judge how much oxygen, hydrogen, sulfur or other elements that a specific nebula contains. The fact that we see a lot of blue stuff in the center of the Rosette Nebula does not mean that this part of the Rosette is completely dominated by oxygen. It means, simply, that an OIII filter (that detects ionized oxygen at 501 nm) has been used on the Rosette Nebula, and wherever oxygen was detected in at least reasonable amounts, the final picture was processed in such a way that "some oxygen" was displayed as "almost all oxygen" and shown as blue.

We have no particular reason to believe that the Rosette Nebula is extremely oxygen-rich.

What does the Rosette Nebula really look like? There are many ways to answer that question, but I like this picture from ESO:

The Rosette Nebula. Credit: ESO/S. Brunier

---

In the ESO/S. Brunier image, you can see that the Rosette Nebula is really faint. It is much fainter than the star cluster that is inside it, NGC 2244, and that is why we see the stars so much clearer than we see the nebula. This is also what it would be like if we observed the Rosette Nebula through a telescope: We would see the stars, but we might not actually see the nebula. And if we did, it would look very faint and round.

One thing is "wrong" with the ESO/S. Brunier image: It shows us the Rosette Nebula as a dull pink object. In reality, we wouldn't see any color in the Rosette Nebula at all.

As a Color Commentator, I have a problem with mapped color images, because the colors in such images don't tell me what I want to know about the objects in question. And quite often, I find the mapped color images aesthetically disappointing.

Bur as to how different photographers have portrayed the Rosette Nebula, I suggest you take a look at this gallery of Rosette Nebula images. Which of all these images shows us the Rosette Nebula as it "really" is?

Well, I still think that the ESO/S Brunier image may be "truer" than any of the images in the gallery, simply because it really brings out the faintness of the nebula. But if you ask me about the images in the gallery, and if you want a "true color image" of the Rosette, you should pick one where the central stars are a very pale shade of blue-white and the surrounding nebula is a very pale shade of pink close to the stars, and much redder farther away from the bright center. One of the first pictures in the gallery, the one by Jean M Dean, is doing a fairly good job at showing these colors to us. Note that the parts of the Rosette that are so glaringly blue in the APOD are grayish-white with a hint of blue in Jean M Dean's image.

The grayish-white color of the inner part of the Rosette Nebula in Jean M Dean's image is a combination of blue-green OIII emission and red hydrogen alpha emission.

So yes, there really is oxygen emission in this part of the Rosette Nebula. Just not in crazy amounts.

Finally, if you want to see a nebula that glows really bright in oxygen emission, you should pick a planetary nebula. Not all planetaries are strongly dominated by oxygen, but some are, and these are the remnants of medium-mass stars that have lost all of their hydrogen during their evolution. Now their cores are blisteringly hot, and the vicinity around the cores is not empty but extremely rarefied, which is perfect for oxygen emission. An example of what these planetaries may look like is this portrait by Adam Block of IC 1295:

Oxygen-rich planetary nebula IC 1295.
Credit: Adam Block.

Ann

[Knight of Clear Skies]

The NGC 2244 star cluster (whose most massive members ionize the Rosette Nebula and make it glow) is not evolved.

I'm probably not using the terminology correctly, but by 'evolved' I mean the nebula is at a late stage of star formation. The stars in the core are on the main sequence and stellar winds are sweeping material from the nebula back into space.

The question I raised above is still relevant, are we seeing a concentration of oxygen in the core because the lighter hydrogen is expelled more easily? Or is the bright OII signal in the centre of the nebula purely down to a higher level of oxygen ionization close to the hot stars?

[AVAO]

It really has that much oxygen (blue) here?
What's the source of this huge oxygen production?

Today's APOD is a mapped color image. While the APOD shows us structures in the Rosette Nebula that are really there, it would be a big mistake to use a mapped color image to try to judge how much oxygen, hydrogen, sulfur or other elements that a specific nebula contains. The fact that we see a lot of blue stuff in the center of the Rosette Nebula does not mean that this part of the Rosette is completely dominated by oxygen. It means, simply, that an OIII filter (that detects ionized oxygen at 501 nm) has been used on the Rosette Nebula, and wherever oxygen was detected in at least reasonable amounts, the final picture was processed in such a way that "some oxygen" was displayed as "almost all oxygen" and shown as blue.

We have no particular reason to believe that the Rosette Nebula is extremely oxygen-rich.

What does the Rosette Nebula really look like? There are many ways to answer that question, but I like this picture from ESO:

The Rosette Nebula. Credit: ESO/S. Brunier

---

In the ESO/S. Brunier image, you can see that the Rosette Nebula is really faint. It is much fainter than the star cluster that is inside it, NGC 2244, and that is why we see the stars so much clearer than we see the nebula. This is also what it would be like if we observed the Rosette Nebula through a telescope: We would see the stars, but we might not actually see the nebula. And if we did, it would look very faint and round.

One thing is "wrong" with the ESO/S. Brunier image: It shows us the Rosette Nebula as a dull pink object. In reality, we wouldn't see any color in the Rosette Nebula at all.

As a Color Commentator, I have a problem with mapped color images, because the colors in such images don't tell me what I want to know about the objects in question. And quite often, I find the mapped color images aesthetically disappointing.

Bur as to how different photographers have portrayed the Rosette Nebula, I suggest you take a look at this gallery of Rosette Nebula images. Which of all these images shows us the Rosette Nebula as it "really" is?

Well, I still think that the ESO/S Brunier image may be "truer" than any of the images in the gallery, simply because it really brings out the faintness of the nebula. But if you ask me about the images in the gallery, and if you want a "true color image" of the Rosette, you should pick one where the central stars are a very pale shade of blue-white and the surrounding nebula is a very pale shade of pink close to the stars, and much redder farther away from the bright center. One of the first pictures in the gallery, the one by Jean M Dean, is doing a fairly good job at showing these colors to us. Note that the parts of the Rosette that are so glaringly blue in the APOD are grayish-white with a hint of blue in Jean M Dean's image.

The grayish-white color of the inner part of the Rosette Nebula in Jean M Dean's image is a combination of blue-green OIII emission and red hydrogen alpha emission.

So yes, there really is oxygen emission in this part of the Rosette Nebula. Just not in crazy amounts.

Finally, if you want to see a nebula that glows really bright in oxygen emission, you should pick a planetary nebula. Not all planetaries are strongly dominated by oxygen, but some are, and these are the remnants of medium-mass stars that have lost all of their hydrogen during their evolution. Now their cores are blisteringly hot, and the vicinity around the cores is not empty but extremely rarefied, which is perfect for oxygen emission. An example of what these planetaries may look like is this portrait by Adam Block of IC 1295:

IC 1295 planetary nebula Adam Block.png

Oxygen-rich planetary nebula IC 1295.
Credit: Adam Block.

Ann

ThanX Ann

As always, your comments are really worth reading! The collection of images at your link "this gallery" is really stunning. That practically every picture looks different, shows that astronomical image processing offers a wide range of color implementation options. But all the more valuable are your assessments.

By the way, my favorite picture from the collection is


Galactic Zoo! by Álvaro Ibáñez Pérez, Pioz, Guadalajara, Spain.

[Ann]

Please remove this post.

[Ann]

The NGC 2244 star cluster (whose most massive members ionize the Rosette Nebula and make it glow) is not evolved.

I'm probably not using the terminology correctly, but by 'evolved' I mean the nebula is at a late stage of star formation. The stars in the core are on the main sequence and stellar winds are sweeping material from the nebula back into space.

The question I raised above is still relevant, are we seeing a concentration of oxygen in the core because the lighter hydrogen is expelled more easily? Or is the bright OII signal in the centre of the nebula purely down to a higher level of oxygen ionization close to the hot stars?

Yes, the OIII emission represents a quite high level of ionization, and it is found close to particularly energetic sources such as O-type stars.

I don't think that the stellar wind from a main sequence O-type star will contain a lot of oxygen, because the photosphere of a main sequence star mostly consists of hydrogen. The wind, at this stage of evolution of the principal stars, will probably not be strongly enriched in oxygen. Frankly, I don't see why it would be.

I found this on the net regarding the composition of the Sun:

By spectroscopy, it is established that if the percentage taken by the relative numbers of atoms is considered then the Sun is made up of 94% hydrogen and 6% of helium, all the other elements add up to about 0.13% of the Sun’s composition.

If the percentage of elements by the total mass of photosphere is observed, the Sun’s chemical composition is 74.9% of hydrogen and 23.8% of helium with other metals accounting for less than 2% of the mass, carbon contributing 0.3%, neon 0.2%, oxygen roughly 1% and iron adding 0.2%.

So 1% of the mass of the Sun's photosphere is made of oxygen. It is not negligible, but it is not a lot.

Maybe you mean that the nebula itself was strongly enriched in oxygen, and the wind from the hot stars mostly blew away the lightweight hydrogen and left more of the somewhat more massive oxygen behind. Yes, a strong stellar wind would indeed work like that, but I still don't see why there should be huge amounts of oxygen in the Rosette Nebula to begin with. Mostly the region near the hot stars of the Rosette Nebula will just be extremely rarefied, because the stellar wind will have blown most of the gases away. It's true, however, that a rarefied medium is exactly what the ionized oxygen needs in order to emit its blue-green light.

But my point, nevertheless, is that there is less oxygen in the Rosette Nebula than the glaringly blue color mapped color of oxygen would lead you to believe.

Ann

[Holger Nielsen]

Ann writes:

"a G2 star"
"an O5 star"

Yes, of course. I'am sure my English teacher taught me this many years ago, forgive an old Dane!
You mention the spectacular image of the Rosetta Nebula by Jean M. Dean. I searched for her on APOD. Her image appeared in fact here in 2019 and was discussed on the Asterisk page.

[Ann]

Ann writes:

"a G2 star"
"an O5 star"

Yes, of course. I'am sure my English teacher taught me this many years ago, forgive an old Dane!
You mention the spectacular image of the Rosetta Nebula by Jean M. Dean. I searched for her on APOD. Her image appeared in fact here in 2019 and was discussed on the Asterisk page.

And I'm an old Swede who is a retired English teacher and a math idiot with a passion for astronomy and, in particular, a passion for the colors of space. I'm sure it comes through in the way I'm lecturing everyone.

Thank you so much for your info on Jean M. Dean! So her image really was an APOD! Indeed, her picture is certainly good enough to be one!

Ann

[Ann]

The NGC 2244 star cluster (whose most massive members ionize the Rosette Nebula and make it glow) is not evolved.

I'm probably not using the terminology correctly, but by 'evolved' I mean the nebula is at a late stage of star formation. The stars in the core are on the main sequence and stellar winds are sweeping material from the nebula back into space.

The question I raised above is still relevant, are we seeing a concentration of oxygen in the core because the lighter hydrogen is expelled more easily? Or is the bright OII signal in the centre of the nebula purely down to a higher level of oxygen ionization close to the hot stars?

Okay, one more for you, Knight of the Clear Skies. You are right that stellar winds can indeed drive hydrogen away selectively from a body of mixed gases. A very good example of this is the atmosphere of Mars.

A solar storm stripping the atmosphere of Mars, breaking up water molecules in the atmosphere and making the 'free hydrogen' leak away into space. Illustration by NASA.

---

However, what we see on Mars is not a thick oxygen atmosphere building up there but a thin CO2 atmosphere being slowly eroded away.

My point is that the interstellar molecular clouds that stars are born from are not dominated by oxygen. They are always dominated by hydrogen.

When a molecular cloud has given birth to stars, these stars will begin blowing their birth nebula away, in the same way that the solar wind is eating away at the atmosphere of Mars. Close to the hottest stars, the nebula will be blown away the fastest. Take a look at this picture of the Christmas Tree Cluster and its main ionizing star, 15 Mon:

15 Mon and the apparent cavity around it, and the Christmas Tree Cluster. Author: I don't know.

---

Take a look at the picture of O-type star 15 Mon and its surrounding nebula. You can clearly see that parts of the red hydrogen alpha nebulosity has been blown away by 15 Mon, so that there is an apparent cavity around 15 Mon. But this cavity isn't empty. If it was, it wouldn't be filled with blue light. The blue color of the cavity must be caused by a combination of scattered blue starlight from 15 Mon and the blue-green glow of ionized oxygen. Because there can be no doubt that there is ionized oxygen in that cavity.

I would say that, yes, the oxygen in that cavity is the result of hydrogen being blown away from 15 Mon more efficiently than oxygen by the stellar winds of 15 Mon. The oxygen was there from the beginning, in the birth nebula of 15 Mon, and it is being retained near the star in the onslaught of the stellar wind more efficiently than hydrogen.

But this still doesn't mean that there are huge amounts of oxygen near 15 Mon. An emission nebula around hot young stars like 15 Mon and the central stars of the Rosette Nebula is something very different than a planetary nebula. In a planetary, all the fluorescing gas around the burned-out stellar core comes from the star itself, as it has ejected all of its innards except for its tiny core. And the star has built up a fairly large amount of oxygen inside itself, before it shrugged off all of its outer layers. It is this "inner oxygen" that glows so brightly green in many planetaries.

Take a look at this great image:

NGC 6543, the Cat's Eye Nebula. Credit: Mathieu Guinot and copyright

---

The fantastic thing about Mathieu Guinot's picture is that it is an RGB image only. Guinot has used no Hα filter, and, what is more remarkable, he has used no OIII filter either. What you see is what you get. This is how green and OIII-rich the Cat's Eye Nebula really is. Because the fluorescing gases of the nebula are the ejected outer layers of the central star itself. And these gases are very highly enriched in oxygen, because the star created this oxygen itself as it was fusing helium into heavier elements during a part of its own evolution.

No emission nebula around hot young stars will ever look like this.

Ann