APOD: Shells and Arcs around Star CW Leonis (2023 Jul 17)

[APOD Robot]

Shells and Arcs around Star CW Leonis

Explanation: What's happening around this star? No one is sure. CW Leonis is the closest carbon star, a star that appears orange because of atmospheric carbon dispersed from interior nuclear fusion. But CW Leonis also appears engulfed in a gaseous carbon-rich nebula. What causes the nebula's complexity is unknown, but its geometry of shells and arcs are surely intriguing. The featured image by the Hubble Space Telescope details this complexity. The low surface gravity of carbon stars enhances their ability to expel carbon and carbon compounds into space. Some of this carbon ends up forming dark dust that is commonly seen in the nebulas of young star-forming regions and the disks of galaxies. Humans and all Earth-based life are carbon-based, and at least some of our carbon was likely once circulating in the atmospheres of near-death stars like carbon stars.

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[shaileshs]

Wow, beautiful image. I wonder what are different objects scene in this photo -
e.g.
1) 4pm (within shells surrounding star) - orange/yellow object with circular dots around
2) 1 pm Orange object
3) 10am top left edge - 2-3 fuzzy galaxy like bluish objects
I wish the photo was published in a way where if we place a mouse on image it'd show various prominent and interesting objects (names/type)..

Maybe experts here in this forum can provide some details ? Thanks to Ann and ChrisP for answers and details to many of my past questions (and in advance for answers to my this and future questions).

[VictorBorun]

4pm (within shells surrounding star) - orange/yellow object with circular dots around

is what's around truly circular?

[VictorBorun]

I wonder if the orange shells we see are in 3d in fact light echoes near our line of sight and who knows how far from CW Leonis

The grazing angle reflection sounds true to explain the orange colour of the carbon dust particles, black as soot and tar.

[Eclectic Man]

"Humans and all Earth-based life are carbon-based, "

Well, we are just as much a water-based life form: "In adult men, about 60% of their bodies are water. However, fat tissue does not have as much water as lean tissue. In adult women, fat makes up more of the body than men, so they have about 55% of their bodies made of water."

From: https://www.usgs.gov/special-topics/wat ... of%20water.

Water is diamagnetic (repels a magnetic field) allowing a physicist / materials scientist to levitate a frog in a magnetic field:

https://www.youtube.com/watch?v=KlJsVqc0ywM

You can try this at home with grapes: https://www.youtube.com/watch?v=D-FNdO4tb-M

[Eric]

Cool pic, thanks. Copyeditor's note: "...its geometry of shells and arcs is surely intriguing." The sentence subject is geometry, which is singular.

[smitty]

I'm surprised no mention was made of the seemingly hexagonal shape of some portions of this image, which are reminiscent of Saturn's polar hexagon. See https://en.wikipedia.org/wiki/Saturn%27s_hexagon . Nature seems to like hexagons.

[De58te]

Just a thought. Carbon fusing stars might not just contain gaseous carbon, but in lower, deeper pressure zones could produce diamonds which is just carbon formed in high pressure into a crystalline form. What if the star is raining diamonds down below and under certain flare conditions blast the diamonds up into the corona. The diamonds being crystals could align themselves into producing the hexagonal light beams. From the Wikipedia diamond page, "Although diamonds are rare on earth, they are quite common in space. Three percent of the carbon in meteorites are in the form of micro diamonds."

[Chris Peterson]

I wonder if the orange shells we see are in 3d in fact light echoes near our line of sight and who knows how far from CW Leonis

The grazing angle reflection sounds true to explain the orange colour of the carbon dust particles, black as soot and tar.

These stars are red for the same reason that sunsets are: wavelength dependent scattering. Not the intrinsic color of the scattering particles. The "soot" preferentially scatters shorter wavelengths of light produce deeper in the star, so only the longer wavelengths (red) make it through.

[VictorBorun]

I wonder if the orange shells we see are in 3d in fact light echoes near our line of sight and who knows how far from CW Leonis

The grazing angle reflection sounds true to explain the orange colour of the carbon dust particles, black as soot and tar.

These stars are red for the same reason that sunsets are: wavelength dependent scattering. Not the intrinsic color of the scattering particles. The "soot" preferentially scatters shorter wavelengths of light produce deeper in the star, so only the longer wavelengths (red) make it through.

then why we see orange at all angle distances from the star rather than red—orange—pale yellow—light gray—pale cyan—blue—dark violet sequence?

[VictorBorun]

Just a thought. Carbon fusing stars might not just contain gaseous carbon, but in lower, deeper pressure zones could produce diamonds which is just carbon formed in high pressure into a crystalline form. What if the star is raining diamonds down below and under certain flare conditions blast the diamonds up into the corona. The diamonds being crystals could align themselves into producing the hexagonal light beams. From the Wikipedia diamond page, "Although diamonds are rare on earth, they are quite common in space. Three percent of the carbon in meteorites are in the form of micro diamonds."

in any case you need
1) some force orienting the dust particles in the same way
2) some plane faces in the surface of a dust particle, like a micro diamond, a piece of graphene film or a soot snowflake

I guess that all the orange shells in this APOD are in fact a small part of the spherical cloud around the carbon star. What "shells" we see are close to our line of sight and the star is mostly behind the "shells" that in fact are rings of reflection between us and the star.
So we do have a force orienting the dust particles in the same direction: it is the stellar wind and the headwind of the interstellar media.

[Chris Peterson]

I wonder if the orange shells we see are in 3d in fact light echoes near our line of sight and who knows how far from CW Leonis

The grazing angle reflection sounds true to explain the orange colour of the carbon dust particles, black as soot and tar.

These stars are red for the same reason that sunsets are: wavelength dependent scattering. Not the intrinsic color of the scattering particles. The "soot" preferentially scatters shorter wavelengths of light produce deeper in the star, so only the longer wavelengths (red) make it through.

then why we see orange at all angle distances from the star rather than red—orange—pale yellow—light gray—pale cyan—blue—dark violet sequence?

The short wavelengths don't escape the star's atmosphere.

[VictorBorun]

These stars are red for the same reason that sunsets are: wavelength dependent scattering. Not the intrinsic color of the scattering particles. The "soot" preferentially scatters shorter wavelengths of light produce deeper in the star, so only the longer wavelengths (red) make it through.

then why we see orange at all angle distances from the star rather than red—orange—pale yellow—light gray—pale cyan—blue—dark violet sequence?

The short wavelengths don't escape the star's atmosphere.

Then the short wavelengths are preferentially absorbed rather than scattered at greater angles. So the colour we see is ink black, slightly orangish.
I mean soot black with no absorption spectrum peak, just micrometer size particles better avoided by longer wavelengths

[Chris Peterson]

then why we see orange at all angle distances from the star rather than red—orange—pale yellow—light gray—pale cyan—blue—dark violet sequence?

The short wavelengths don't escape the star's atmosphere.

Then the short wavelengths are preferentially absorbed rather than scattered at greater angles. So the colour we see is ink black, slightly orangish.
I mean soot black with no absorption spectrum peak, just micrometer size particles better avoided by longer wavelengths

Scattering is the fundamental phenomenon, not absorption. Absorption is secondary to scattering, and is a simple consequence of the much longer travel path for short wavelength photons.

[Ann]

Wow, beautiful image. I wonder what are different objects scene in this photo -
e.g.
1) 4pm (within shells surrounding star) - orange/yellow object with circular dots around
2) 1 pm Orange object
3) 10am top left edge - 2-3 fuzzy galaxy like bluish objects
I wish the photo was published in a way where if we place a mouse on image it'd show various prominent and interesting objects (names/type)..

Maybe experts here in this forum can provide some details ? Thanks to Ann and ChrisP for answers and details to many of my past questions (and in advance for answers to my this and future questions).

I uploaded the "square ring galaxy" to my computer already in 2021! It is a very striking object.

This is clearly a barred ring galaxy, where the ring, for some reason, looks amazingly square. It is possible that the blue object just above it is a satellite galaxy affecting the ring galaxy through tidal effects, but I don't think that is the likeliest explanation. I find it more likely that the ring galaxy has "distorted itself" by means of its own star formation. Also it's possible that the square-looking shape is actually caused by an overlapping spiral arm.

Consider galaxy M61:

M61 in optical light (left) and in molecular gas. Credit: ESO/ALMA (ESO/NAOJ/NRAO)/PHANGS

---

In the picture at left, you can see M61 in optical light. Note the angular shape of the spiral arms. But in the picture at right, M61 has been photographed at a wavelength that detects the galaxy's molecular gas. Note that the image at right looks a lot less angular. This means that it is mostly "the brilliant fluff" of the galaxy, the raging but superficial star formation, that makes the arms of M61 look angular. The underlying galactic structure of molecular gas, dust and low-mass stars is a lot smoother.

Galaxies are distorted by strong bouts of star formation, and I find it likely that the ring galaxy behind CW Leonis has distorted itself by this manner.


You asked about the orange light at 1 o'clock. That is almost certainly a star. What looks like a galactic disk surrounding it is almost certainly the sort of spikes and halos that are seen surrounding all the stars in this image.

You also asked about "10am top left edge - 2-3 fuzzy galaxy like bluish objects". Not sure what you mean by that, but please note that there are small blue objects scattered all over the image. These are distant starforming galaxies whose brilliant ultraviolet light has been redshifted so that they look blue to us. Or do they actually look so blue?

No, unfortunately not. Go to this page and scroll down until you see "Colours and filters" at lower right. Here you can see that one of the filters used for this image was a wideband one centered on 606 nm, which is this color: ███. As you can see, it's not the least bit blue. But it is still the "bluest", i.e. the most short-wave sensitive, of the filters used for the image of CW Leonis, since the other two filters are infrared-sensitive ones.

So in other words, the galaxies that look blue, i.e., their ultraviolet light may in fact be redshifted so that it peaks somewhere between 400 and 500 nm, which will indeed make them look blue: ███. But many other redshifted colors are possible, including, for example, this one: ███. With the filters used for the CW Leonis image, a beige-looking background galaxy would still probably be mapped as blue!

The thing to remember is that all the blue-looking background galaxies in the CW Leonis image contain brilliantly bright and extremely hot O-stars which produce copious amounts of ultraviolet light. This ultraviolet light been redshifted into longer wavelengths before it reaches us.

Hope that helped!

Ann

[VictorBorun]

so much for my "orange soot ink" claim

[JamesM]

I'm surprised no mention was made of the seemingly hexagonal shape of some portions of this image, which are reminiscent of Saturn's polar hexagon.

Very intriguing observation, Smitty. I think you very well could be onto something here.

So from your point of view, a polar hexagon would be pointing in our direction, and this star is blowing smoke rings out of its polar hexagon at us?

[johnnydeep]

Lots of VERY interesting background galaxies stealing the show, IMO, and conveniently arrayed all around it, like fireflies around a camp fire!

But a basic question: what does the "CW" mean in CW Leonis? What's the convention being followed here?

[orin stepanek]

Indeed a very unusual looking star!

[Chris Peterson]

Lots of VERY interesting background galaxies stealing the show, IMO, and conveniently arrayed all around it, like fireflies around a camp fire!

But a basic question: what does the "CW" mean in CW Leonis? What's the convention being followed here?

It's a friggin historical mess: https://en.wikipedia.org/wiki/Variable_star_designation

[AVAO]

I'm surprised no mention was made of the seemingly hexagonal shape of some portions of this image, which are reminiscent of Saturn's polar hexagon.

Very intriguing observation, Smitty. I think you very well could be onto something here.

So from your point of view, a polar hexagon would be pointing in our direction, and this star is blowing smoke rings out of its polar hexagon at us?

Saturn's Strange Hexagon Recreated in the Lab...
https://www.science.org/content/article ... reated-lab
video: https://www.youtube.com/watch?v=n_c9A9Auf0A&t=32s

I don't think it is the same mechanism.
Corners can also occur when filaments twist into each other or if they are "lit" from a specific angle.
https://esahubble.org/videos/heic2112a/

Click to view full size image

Maybe there are other reasons for the shell-like structure around CW Leonis.

Herschel:

Click to view full size image

Galaxy Evolution Explorer:

Click to view full size image

"CW Leonis is a runaway star, plowing through the depths of space and piling up interstellar material before it, can be seen in this ultraviolet image from NASA's Galaxy Evolution Explorer. The star is hurtling through space at about 204,000 miles per hour (91 kilometers per second), or roughly 265 times the speed of sound on Earth. It is shedding its own atmosphere to form a sooty shell of discarded material. This shell can be seen in the center of this image as a bright circular blob."
NASA/JPL-Caltech (https://www.jpl.nasa.gov/images/pia15417-cw-leo)

[AVAO]

...
I uploaded the "square ring galaxy" to my computer already in 2021! It is a very striking object.
...
This is clearly a barred ring galaxy, where the ring, for some reason, looks amazingly square. It is possible that the blue object just above it is a satellite galaxy affecting the ring galaxy through tidal effects, but I don't think that is the likeliest explanation. I find it more likely that the ring galaxy has "distorted itself" by means of its own star formation. Also it's possible that the square-looking shape is actually caused by an overlapping spiral arm.
...
Ann

ThanX Ann

Parallelogram like appearances may also appear visually when spiral arms twist against each other, as in the core area of Centaurus A, where this effect is only visible in the infrared.


https://upload.wikimedia.org/wikipedia/ ... nearIR.jpg

[VictorBorun]

...
I uploaded the "square ring galaxy" to my computer already in 2021! It is a very striking object.
...
This is clearly a barred ring galaxy, where the ring, for some reason, looks amazingly square. It is possible that the blue object just above it is a satellite galaxy affecting the ring galaxy through tidal effects, but I don't think that is the likeliest explanation. I find it more likely that the ring galaxy has "distorted itself" by means of its own star formation. Also it's possible that the square-looking shape is actually caused by an overlapping spiral arm.
...
Ann

ThanX Ann

Parallelogram like appearances may also appear visually when spiral arms twist against each other, as in the core area of Centaurus A, where this effect is only visible in the infrared.


https://upload.wikimedia.org/wikipedia/ ... nearIR.jpg

the rectangular which are in fact the curved circular viewed at an angle?
Kokichi Sugihara before his mirror:

Click to play embedded YouTube video.

[VictorBorun]

Here is a parallel-view Stereogram 3D of a spiral or a tunnel close to our line of sight:



I think this is what the shells in this APOD are in 3d
But how come the cross-section of the tube is hexagonal I am at loss

[Ann]

Lots of VERY interesting background galaxies stealing the show, IMO, and conveniently arrayed all around it, like fireflies around a camp fire!

But a basic question: what does the "CW" mean in CW Leonis? What's the convention being followed here?

"CW" just means that this is a variable star in constellation Leo, and it is not the first variable star discovered in this constellation - far from it!

The first discovered variable star in a constellation gets the letter "R", followed by the constellation name in genitiv form. One example is R Corona Borealis. The next letter for a variable star in a constellation, after R is taken, is S, as in S Monocerotis. Then we have T, as in T Lyrae.

There are variable stars with designations beginning on U, V and W too, although I can't remember one beginning on Z.

After these letters are used up, variable stars get double-letter names, as in AE Aurigae. Even novas can get double-letter names like these, such as GK Persei.

Read about the naming of variable stars here.

Ann