APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 3693
Joined: Fri Dec 04, 2009 3:27 am

APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by APOD Robot » Sun Sep 29, 2019 4:09 am

Image MyCn 18: The Engraved Hourglass Planetary Nebula

Explanation: Do you see the hourglass shape -- or does it see you? If you can picture it, the rings of MyCn 18 trace the outline of an hourglass -- although one with an unusual eye in its center. Either way, the sands of time are running out for the central star of this hourglass-shaped planetary nebula. With its nuclear fuel exhausted, this brief, spectacular, closing phase of a Sun-like star's life occurs as its outer layers are ejected - its core becoming a cooling, fading white dwarf. In 1995, astronomers used the Hubble Space Telescope (HST) to make a series of images of planetary nebulae, including the one featured here. Pictured, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the hourglass. The unprecedented sharpness of the Hubble images has revealed surprising details of the nebula ejection process that are helping to resolve the outstanding mysteries of the complex shapes and symmetries of planetary nebulas like MyCn 18.

<< Previous APOD This Day in APOD Next APOD >>

User avatar
Ann
4725 Å
Posts: 9815
Joined: Sat May 29, 2010 5:33 am

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by Ann » Sun Sep 29, 2019 4:37 am

Since I'm the first to post here, I should say something nice. Particularly since you processed the image, Geck.

But there is something about the colors of this image that weirds me out. The Engraved Hourglass Nebula looks strange in any case, but when the colors also strike me as "wrong", the emotional part of me just rejects the image. The rational part of me tells me that I'm being stupid and childish beyond words, because if there is anything that is well suited for narrowband photography and mapped color images it is nebulas, which shine in narrowband light anyway.

The emotional part tells me that come on, since when is hydrogen alpha emission green? And, please tell me, since when is the ionizing star of a planetary nebula pink? The rational part of me tells me that I'm sulking like a kid, and that I'm acting like a kid, which is very unattractive at my age. And the emotional part of me says, You know what? I don't believe in this picture anyway!!! Give me a nice RGB image of this thing and I'll believe in it!!

And the rational part of me says, You old drama queen. As if you don't believe in this image. As if.

Ann
Color Commentator

User avatar
geckzilla
Ocular Digitator
Posts: 8987
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by geckzilla » Sun Sep 29, 2019 5:58 am

It would be very red even in an RGB image. The center would be green, yellow, or white, depending on how the colors were balanced. There really is some [O III] emission in the center..
Just call me "geck" because "zilla" is like a last name.

De58te
Science Officer
Posts: 280
Joined: Mon Sep 30, 2013 6:35 pm

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by De58te » Sun Sep 29, 2019 10:42 am

It is also very unusual for it to take the shape of an hourglass, since most pictures of planetary nebula I seen blow out horizontally, left to right. Making them appear like binoculars or like the infinity symbol.

User avatar
JohnD
Tea Time, Guv! Cheerio!
Posts: 1173
Joined: Wed Feb 16, 2005 2:11 pm
Location: Lancaster, England

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by JohnD » Sun Sep 29, 2019 11:42 am

Really?

Look here: https://www.skyandtelescope.com/observi ... y-nebulae/ for PNs in their infinite variety.
John

User avatar
orin stepanek
Plutopian
Posts: 5049
Joined: Wed Jul 27, 2005 3:41 pm
Location: Nebraska

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by orin stepanek » Sun Sep 29, 2019 12:05 pm

I like it! I'll have a wallpaper for my computer for a day1 8-)
MyCn18_HubbleSchmidt_960.jpg
You do not have the required permissions to view the files attached to this post.
Orin

Smile today; tomorrow's another day!

BDanielMayfield
Don't bring me down
Posts: 2133
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by BDanielMayfield » Sun Sep 29, 2019 12:53 pm

Ann wrote:
Sun Sep 29, 2019 4:37 am
Since I'm the first to post here, I should say something nice. Particularly since you processed the image, Geck.

But there is something about the colors of this image that weirds me out. The Engraved Hourglass Nebula looks strange in any case, but when the colors also strike me as "wrong", the emotional part of me just rejects the image. The rational part of me tells me that I'm being stupid and childish beyond words, because if there is anything that is well suited for narrowband photography and mapped color images it is nebulas, which shine in narrowband light anyway.

The emotional part tells me that come on, since when is hydrogen alpha emission green? And, please tell me, since when is the ionizing star of a planetary nebula pink? The rational part of me tells me ...
Well at least you are open and honest in your appraisal Ann. I personally think it's a fine rendering, thanks for producing it geck. I'll rationally answer that a white dwarf embedded inside a PN can have its light reddened by the dust in front of it. It looks to me like the bottom half of the nebula is the side moving toward us, and thus we are seeing the central star through a thick belt of dust.

Bruce
"Happy are the peaceable ... "

User avatar
Chris Peterson
Abominable Snowman
Posts: 14561
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by Chris Peterson » Sun Sep 29, 2019 1:56 pm

Ann wrote:
Sun Sep 29, 2019 4:37 am
And, please tell me, since when is the ionizing star of a planetary nebula pink?
The ionizing star of a planetary nebula is always pink in images in nitrogen/hydrogen/oxygen data processed with this standard palette. This is a much more useful way of visualizing planetary nebulas than in red/green/blue.

The apparent color of elements in any image is not important if we understand what those colors mean.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Chris Peterson
Abominable Snowman
Posts: 14561
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by Chris Peterson » Sun Sep 29, 2019 2:00 pm

De58te wrote:
Sun Sep 29, 2019 10:42 am
It is also very unusual for it to take the shape of an hourglass, since most pictures of planetary nebula I seen blow out horizontally, left to right. Making them appear like binoculars or like the infinity symbol.
There are quite a lot of planetary nebulas that look similar to this. Most planetaries fall into one of two categories- they produce a fairly symmetric shell (a bubble) or they produce a fairly symmetric pair of lobes. The latter will only look like an infinity symbol if we happen to view them perfectly perpendicular to the lobes. In most cases, as here, we see the structure at some angle, and get the hourglass effect instead.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
geckzilla
Ocular Digitator
Posts: 8987
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by geckzilla » Sun Sep 29, 2019 3:22 pm

Keep in mind the central star, which is quite a bit off center, might not actually be the progenitor. I mean, given the current information it is likely, but if we could get some high resolution near-infrared imagery, we could rule out a hidden star. These nebulas do tend to have a thick central torus of dust that could be obscuring another star. None of the infrared imagery we have so far can resolve such a thing, though. The whole nebula glows in infrared, so we need a telescope like Hubble to look, but no one has done so and no one plans to.
Just call me "geck" because "zilla" is like a last name.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 16338
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by neufer » Sun Sep 29, 2019 5:35 pm

https://en.wikipedia.org/wiki/The_Great_Gatsby wrote:

<<The cover of the first printing of The Great Gatsby is among the most celebrated pieces of art in American literature. It depicts disembodied eyes and a mouth over a blue skyline, with images of naked women reflected in the irises. A little-known artist named Francis Cugat was commissioned to illustrate the book while Fitzgerald was in the midst of writing it. The cover was completed before the novel, and Fitzgerald was so enamored with it that he told his publisher he had "written it into" the novel. Fitzgerald's remarks about incorporating the painting into the novel led to the interpretation that the eyes are reminiscent of those of fictional optometrist Dr. T. J. Eckleburg, depicted on a faded commercial billboard near George Wilson's auto repair shop, which Fitzgerald described as:

blue and gigantic—their retinas[e] are one yard high. They look out of no face, but instead, from a pair of enormous yellow spectacles which pass over a non-existent nose. >>
Art Neuendorffer

User avatar
Ann
4725 Å
Posts: 9815
Joined: Sat May 29, 2010 5:33 am

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by Ann » Sun Sep 29, 2019 7:14 pm

Chris Peterson wrote:
Sun Sep 29, 2019 1:56 pm
Ann wrote:
Sun Sep 29, 2019 4:37 am
And, please tell me, since when is the ionizing star of a planetary nebula pink?
The ionizing star of a planetary nebula is always pink in images in nitrogen/hydrogen/oxygen data processed with this standard palette. This is a much more useful way of visualizing planetary nebulas than in red/green/blue.

The apparent color of elements in any image is not important if we understand what those colors mean.

I know, Chris. Don't I know it. Ann
Color Commentator

TheOtherBruce
Ensign
Posts: 45
Joined: Wed Jul 17, 2019 6:07 pm

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by TheOtherBruce » Sun Sep 29, 2019 10:29 pm

Chris Peterson wrote:
Sun Sep 29, 2019 1:56 pm
The ionizing star of a planetary nebula is always pink in images in nitrogen/hydrogen/oxygen data processed with this standard palette.
I'm probably missing something obvious, but I've always wondered why those three elements in particular (well, the nitrogen and oxygen anyway) are chosen so often to make up these narrowband images. Is it just that these gases make up the largest proportion of the ejected material, so they'd make a brighter, better image? Are their emission lines arranged so that they're the easiest to collect narrowband data from? Something else?
This universe shipped by weight, not by volume.
Some expansion of the contents may have occurred during shipment.

User avatar
AVAO
Ensign
Posts: 27
Joined: Tue May 28, 2019 12:24 pm
AKA: multiwavelength traveller
Location: Zurich

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by AVAO » Sun Sep 29, 2019 10:47 pm

Below I try to compare a close-up from the core with the ring nebula. I think these type of planetary nebula are missing the hourglass ejection surfaces, as they have already dissolved. Therefore you can only see the central ring. The typical eye-like formation in the case of MyCn 18 results from the specific angle of view.

Jack from the AVAO team
[/quote]

User avatar
neufer
Vacationer at Tralfamadore
Posts: 16338
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by neufer » Mon Sep 30, 2019 4:41 pm

TheOtherBruce wrote:
Sun Sep 29, 2019 10:29 pm
Chris Peterson wrote:
Sun Sep 29, 2019 1:56 pm

The ionizing star of a planetary nebula is always pink in images in nitrogen/hydrogen/oxygen data processed with this standard palette.
I'm probably missing something obvious, but I've always wondered why those three elements in particular (well, the nitrogen and oxygen anyway) are chosen so often to make up these narrowband images. Is it just that these gases make up the largest proportion of the ejected material, so they'd make a brighter, better image? Are their emission lines arranged so that they're the easiest to collect narrowband data from? Something else?
Excellent question, Bruce :!:

The gases thrown off by these geriatric Sun-like stars simply
reflect the abundances of the elements in the Solar System :arrow:
I.e., mostly: Hydrogen, Helium, Oxygen, Carbon, Nitrogen & Neon.


Such gases are all capable of producing relatively broad emission lines as excited electrons drop rapidly to lower energy states.

However: most noticeable above the visible background (other than Balmer hydrogen lines)
are the very narrow forbidden lines of ionized oxygen & nitrogen.
https://en.wikipedia.org/wiki/Forbidden_mechanism#In_astrophysics_and_atomic_physics wrote:
<<Forbidden emission lines have been observed in extremely low-density gases and plasmas, either in outer space or in the extreme upper atmosphere of the Earth. In space environments, densities may be only a few atoms per cubic centimetre, making atomic collisions unlikely. Under such conditions, once an atom or molecule has been excited for any reason into a meta-stable state, then it is almost certain to decay by emitting a forbidden-line photon. Since meta-stable states are rather common, forbidden transitions account for a significant percentage of the photons emitted by the ultra-low density gas in space. Forbidden transitions in highly charged ions resulting in the emission of visible, vacuum-ultraviolet, soft x-ray and x-ray photons are routinely observed in certain laboratory devices such as electron beam ion traps and ion storage rings, where in both cases residual gas densities are sufficiently low for forbidden line emission to occur before atoms are collisionally de-excited. Using laser spectroscopy techniques, forbidden transitions are used to stabilize atomic clocks and quantum clocks that have the highest accuracies currently available.

Forbidden lines of nitrogen ([N II] at 654.8 and 658.4 nm), sulfur ({S II} at 671.6 and 673.1 nm), and oxygen ([O II] at 372.7 nm, and [O III] at 495.9 and 500.7 nm) are commonly observed in astrophysical plasmas. These lines are important to the energy balance of planetary nebulae and H II regions. The forbidden 21-cm hydrogen line is particularly important for radio astronomy as it allows very cold neutral hydrogen gas to be seen. Also, the presence of [O I] and {S II} forbidden lines in the spectra of T-tauri stars implies low gas density.

Forbidden line transitions are noted by placing square brackets around the atomic or molecular species in question, e.g. [O III] or {S II}.>>
Art Neuendorffer

TheOtherBruce
Ensign
Posts: 45
Joined: Wed Jul 17, 2019 6:07 pm

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by TheOtherBruce » Mon Sep 30, 2019 8:37 pm

neufer wrote:
Mon Sep 30, 2019 4:41 pm

The gases thrown off by these geriatric Sun-like stars simply
reflect the abundances of the elements in the Solar System :arrow:
I.e., mostly: Hydrogen, Helium, Oxygen, Carbon, Nitrogen & Neon.
Interesting, I haven't seen the element abundances set out in a graph like this before. Much easier to visualise.

Now that I've seen it like this, I'm wondering about the relatively tiny amounts of Lithium, Beryllium and Boron, compared to Helium and Carbon. All the other elements seem to (mostly) follow a neat decay curve. A bit of Wiki diving showed that these elements are much more commonly made by cosmic ray spallation of heavier atoms than by actual nucleosynthesis. Any idea why nucleosynthesis is such a low-probability event? It's also (to me, anyway) downright weird that all the even atomic numbers are more abundant than the odd numbers next to them.
This universe shipped by weight, not by volume.
Some expansion of the contents may have occurred during shipment.

User avatar
geckzilla
Ocular Digitator
Posts: 8987
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by geckzilla » Mon Sep 30, 2019 8:38 pm

AVAO wrote:
Sun Sep 29, 2019 10:47 pm
Below I try to compare a close-up from the core with the ring nebula. I think these type of planetary nebula are missing the hourglass ejection surfaces, as they have already dissolved. Therefore you can only see the central ring. The typical eye-like formation in the case of MyCn 18 results from the specific angle of view.

Jack from the AVAO team
Those two nebulas look similar when you crop and rotate them to match, but MyCn 18 likely at a much younger stage. NGC 3132 is probably older and in a less organized stage.
Just call me "geck" because "zilla" is like a last name.

User avatar
geckzilla
Ocular Digitator
Posts: 8987
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by geckzilla » Mon Sep 30, 2019 8:39 pm

AVAO wrote:
Sun Sep 29, 2019 10:47 pm
Below I try to compare a close-up from the core with the ring nebula. I think these type of planetary nebula are missing the hourglass ejection surfaces, as they have already dissolved. Therefore you can only see the central ring. The typical eye-like formation in the case of MyCn 18 results from the specific angle of view.

Jack from the AVAO team
Those two nebulas look similar when you crop and rotate them to match, but MyCn 18 likely at a much younger stage. NGC 3132 is probably older and in a less organized stage. I don't think the same thing is causing the star appear off center, and the two apparent ringlike structures are only incidentally similar.
Just call me "geck" because "zilla" is like a last name.

TheOtherBruce
Ensign
Posts: 45
Joined: Wed Jul 17, 2019 6:07 pm

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by TheOtherBruce » Mon Sep 30, 2019 8:45 pm

geckzilla wrote:
Mon Sep 30, 2019 8:39 pm
Those two nebulas look similar when you crop and rotate them to match, but MyCn 18 likely at a much younger stage. NGC 3132 is probably older and in a less organized stage. I don't think the same thing is causing the star appear off center, and the two apparent ringlike structures are only incidentally similar.
I dunno, I get the impression that these two are also roughly hourglass/dumbell shaped, it's just that we're looking "down the throat" so that they seem roundish or oval.
This universe shipped by weight, not by volume.
Some expansion of the contents may have occurred during shipment.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 16338
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by neufer » Mon Sep 30, 2019 9:02 pm

geckzilla wrote:
Mon Sep 30, 2019 8:39 pm

Those two nebulas look similar when you crop and rotate them to match, but MyCn 18 likely at a much younger stage. NGC 3132 is probably older and in a less organized stage. I don't think the same thing is causing the star appear off center, and the two apparent ringlike structures are only incidentally similar.
It is interesting that the NGC 3132 PNN is the faint companion of the apparent PNN:
https://en.wikipedia.org/wiki/NGC_3132 wrote: <<NGC 3132, also known as the Eight-Burst Nebula, the Southern Ring Nebula, is a bright and extensively studied planetary nebula in the constellation Vela. Its distance from Earth is estimated at about 2,000 light-years.

Images of NGC 3132 reveal two stars close together within the nebulosity, one of 10th magnitude, the other 16th. The central planetary nebula nucleus (PNN) or white dwarf central star is the fainter of these two stars. This hot central star of about 100,000 K has now blown off its layers and is making the nebula fluoresce brightly from the emission of its intense ultraviolet radiation.>>
Art Neuendorffer

User avatar
geckzilla
Ocular Digitator
Posts: 8987
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by geckzilla » Mon Sep 30, 2019 9:20 pm

TheOtherBruce wrote:
Mon Sep 30, 2019 8:45 pm
geckzilla wrote:
Mon Sep 30, 2019 8:39 pm
Those two nebulas look similar when you crop and rotate them to match, but MyCn 18 likely at a much younger stage. NGC 3132 is probably older and in a less organized stage. I don't think the same thing is causing the star appear off center, and the two apparent ringlike structures are only incidentally similar.
I dunno, I get the impression that these two are also roughly hourglass/dumbell shaped, it's just that we're looking "down the throat" so that they seem roundish or oval.
You can see more details in the Hubble version showing that it is not merely a cylinder, barrel, or hourglass. It is irregularly shaped, though the central blue area does seem to form a spheroid. Either way, the point here is that looking at a much younger pre planetary nebula versus an older regular planetary nebula is not going to help you much. Not only is the scale different, the nebula has continued its progress beyond its initial stage. It's not prudent to find some superficially similar photos and then conclude that they must therefore be similar.

Take a look at NGC 3132: https://flic.kr/p/gJ3NzH
Image
Just call me "geck" because "zilla" is like a last name.

BDanielMayfield
Don't bring me down
Posts: 2133
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by BDanielMayfield » Tue Oct 01, 2019 1:39 am

TheOtherBruce wrote:
Mon Sep 30, 2019 8:37 pm
neufer wrote:
Mon Sep 30, 2019 4:41 pm

The gases thrown off by these geriatric Sun-like stars simply
reflect the abundances of the elements in the Solar System :arrow:
I.e., mostly: Hydrogen, Helium, Oxygen, Carbon, Nitrogen & Neon.
Interesting, I haven't seen the element abundances set out in a graph like this before. Much easier to visualise.

Now that I've seen it like this, I'm wondering about the relatively tiny amounts of Lithium, Beryllium and Boron, compared to Helium and Carbon. All the other elements seem to (mostly) follow a neat decay curve. A bit of Wiki diving showed that these elements are much more commonly made by cosmic ray spallation of heavier atoms than by actual nucleosynthesis. Any idea why nucleosynthesis is such a low-probability event? It's also (to me, anyway) downright weird that all the even atomic numbers are more abundant than the odd numbers next to them.
The light elements Li, Be and B get created in stars, but they then ether decay back into something smaller due to instabilities or are promptly fused into something with stability, typically Carbon12. Consider this from wikipedia under "Triple Alpha Process":
The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon.[1][2]

Helium accumulates in the core of stars as a result of the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle. Further nuclear fusion reactions of helium with hydrogen or another alpha particle produce lithium-5 and beryllium-8 respectively. Both products are highly unstable and decay almost instantly back into smaller nuclei, unless a third alpha particle fuses with a beryllium-8 nucleus before that time to produce a stable carbon-12 nucleus. The half-life of 5Li is 3.7×10−22 s and that of 8Be is 8.19×10−17 s.[3] When a star runs out of hydrogen to fuse in its core, it begins to contract and heat up. If the central temperature rises to 108 K,[4] six times hotter than the Sun's core, alpha particles can fuse fast enough to produce significant amounts of carbon:

4 2He + 4 2He → 8 4Be
(−0.0918 MeV)
8 4Be + 4 2He → 12 6C + 2 γ
(+7.367 MeV)
The net energy release of the process is 7.275 MeV.

As a side effect of the process, some carbon nuclei fuse with additional helium to produce a stable isotope of oxygen and energy:

12 6C + 4 2He → 16 8O + γ
(+7.162 MeV)

Fusing with additional helium nuclei can create heavier elements in a chain of stellar nucleosynthesis known as the alpha process, but these reactions are only significant at higher temperatures and pressures than in cores undergoing the triple-alpha process. This creates a situation in which stellar nucleosynthesis produces large amounts of carbon and oxygen but only a small fraction of those elements are converted into neon and heavier elements. Oxygen and carbon make up the main "ash" of helium-4 burning.
The continuing additions of 2 proton alpha particles is what accounts for the preponderance of the even numbered elements.

Bruce
"Happy are the peaceable ... "

User avatar
AVAO
Ensign
Posts: 27
Joined: Tue May 28, 2019 12:24 pm
AKA: multiwavelength traveller
Location: Zurich

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by AVAO » Tue Oct 01, 2019 9:59 am

geckzilla wrote:
Mon Sep 30, 2019 8:39 pm
AVAO wrote:
Sun Sep 29, 2019 10:47 pm
Below I try to compare a close-up from the core with the ring nebula. I think these type of planetary nebula are missing the hourglass ejection surfaces, as they have already dissolved. Therefore you can only see the central ring. The typical eye-like formation in the case of MyCn 18 results from the specific angle of view.

Jack from the AVAO team
Those two nebulas look similar when you crop and rotate them to match, but MyCn 18 likely at a much younger stage. NGC 3132 is probably older and in a less organized stage. I don't think the same thing is causing the star appear off center, and the two apparent ringlike structures are only incidentally similar.
ThanX Geck for your detailed comments and sharing your great work. I think your picture is much more "realistic" than the first "green-eye" NASA release. Basically you are absolutely right. The comparison was only intended as an example. There are a variety of ring-shaped planetary nebulae. My hypothesis was only, that they are older - as you say - so that only the nearer areas around the star stay illuminated, but not the much larger hourglass-shaped wings (red in your picture) we known from young planetary nebulae...

User avatar
neufer
Vacationer at Tralfamadore
Posts: 16338
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by neufer » Tue Oct 01, 2019 4:44 pm

BDanielMayfield wrote:
Tue Oct 01, 2019 1:39 am

The continuing additions of 2 proton alpha particles is what accounts for the preponderance of the even numbered elements.
neufer wrote:
Tue Oct 01, 2019 3:04 am

3) Any sufficiently advanced [nuclear] technology is indistinguishable from Magic.

viewtopic.php?f=23&t=18222&p=295701#p295701
https://en.wikipedia.org/wiki/Magic_number_(physics) wrote:

<<In nuclear physics, a magic number is a number of nucleons (either protons or neutrons, separately) such that they are arranged into complete shells within the atomic nucleus. The seven most widely recognized magic numbers as of 2019 are 2, 8, 20, 28, 50, 82, and 126. For protons, this corresponds to the elements helium, oxygen, calcium, nickel, tin, lead and the hypothetical unbihexium, although 126 is so far only known to be a magic number for neutrons. Atomic nuclei consisting of such a magic number of nucleons have a higher average binding energy per nucleon than one would expect based upon predictions such as the semi-empirical mass formula and are hence more stable against nuclear decay.

The unusual stability of isotopes having magic numbers means that transuranium elements could theoretically be created with extremely large nuclei and yet not be subject to the extremely rapid radioactive decay normally associated with high atomic numbers. Large isotopes with magic numbers of nucleons are said to exist in an island of stability. Unlike the magic numbers 2–126, which are realized in spherical nuclei, theoretical calculations predict that nuclei in the island of stability are deformed. Before this was realized, higher magic numbers, such as 184, 258, 350, and 462 (sequence A033547 in the OEIS), were predicted based on simple calculations that assumed spherical shapes. It is now believed that the sequence of spherical magic numbers cannot be extended in this way. Further predicted magic numbers are 114, 122, 124, and 164 for protons as well as 184, 196, 236, and 318 for neutrons.>>
Art Neuendorffer

User avatar
neufer
Vacationer at Tralfamadore
Posts: 16338
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: MyCn 18: The Engraved Hourglass... (2019 Sep 29)

Post by neufer » Tue Oct 01, 2019 6:05 pm

BDanielMayfield wrote:
Tue Oct 01, 2019 1:39 am

The continuing additions of 2 proton alpha particles is what accounts for the preponderance of the even numbered elements.
https://en.wikipedia.org/wiki/Nuclear_binding_energy wrote:
<<In the periodic table of elements, the series of light elements from hydrogen up to sodium is observed to exhibit generally increasing binding energy per nucleon as the atomic mass increases. This increase is generated by increasing forces per nucleon in the nucleus, as each additional nucleon is attracted by other nearby nucleons, and thus more tightly bound to the whole.

The region of increasing binding energy is followed by a region of relative stability (saturation) in the sequence from magnesium through xenon. In this region, the nucleus has become large enough that nuclear forces no longer completely extend efficiently across its width. Attractive nuclear forces in this region, as atomic mass increases, are nearly balanced by repellent electromagnetic forces between protons, as the atomic number increases. Finally, in elements heavier than xenon, there is a decrease in binding energy per nucleon as atomic number increases. In this region of nuclear size, electromagnetic repulsive forces are beginning to overcome the strong nuclear force attraction.

At the peak of binding energy, nickel-62 is the most tightly bound nucleus (per nucleon), followed by iron-58 and iron-56. This is the approximate basic reason why iron and nickel are very common metals in planetary cores, since they are produced profusely as end products in supernovae and in the final stages of silicon burning in stars. However, it is not binding energy per defined nucleon (as defined above), which controls which exact nuclei are made, because within stars, neutrons are free to convert to protons to release even more energy, per generic nucleon, if the result is a stable nucleus with a larger fraction of protons. In fact, it has been argued that photodisintegration of 62Ni to form 56Fe may be energetically possible in an extremely hot star core, due to this beta decay conversion of neutrons to protons. The conclusion is that at the pressure and temperature conditions in the cores of large stars, energy is released by converting all matter into 56Fe nuclei (ionized atoms). (However, at high temperatures not all matter will be in the lowest energy state.) This energetic maximum should also hold for ambient conditions, say T = 298 K and p = 1 atm, for neutral condensed matter consisting of 56Fe atoms—however, in these conditions nuclei of atoms are inhibited from fusing into the most stable and low energy state of matter.

It is generally believed that iron-56 is more common than nickel isotopes in the universe for mechanistic reasons, because its unstable progenitor nickel-56 is copiously made by staged build-up of 14 helium nuclei inside supernovas, where it has no time to decay to iron before being released into the interstellar medium in a matter of a few minutes, as the supernova explodes. However, nickel-56 then decays to cobalt-56 within a few weeks, then this radioisotope finally decays to iron-56 with a half life of about 77.3 days. The radioactive decay-powered light curve of such a process has been observed to happen in type II supernovae, such as SN 1987A. In a star, there are no good ways to create nickel-62 by alpha-addition processes, or else there would presumably be more of this highly stable nuclide in the universe.>>
https://en.wikipedia.org/wiki/Lithium#Astronomical wrote:
<<Though it was synthesized in the Big Bang, lithium (together with beryllium and boron) is markedly less abundant in the universe than other elements. This is a result of the comparatively low stellar temperatures necessary to destroy lithium, along with a lack of common processes to produce it.

According to modern cosmological theory, lithium—in both stable isotopes (lithium-6 and lithium-7)—was one of the three elements synthesized in the Big Bang. Though the amount of lithium generated in Big Bang nucleosynthesis is dependent upon the number of photons per baryon, for accepted values the lithium abundance can be calculated, and there is a "cosmological lithium discrepancy" in the universe: older stars seem to have less lithium than they should, and some younger stars have much more. The lack of lithium in older stars is apparently caused by the "mixing" of lithium into the interior of stars, where it is destroyed, while lithium is produced in younger stars. Though it transmutes into two atoms of helium due to collision with a proton at temperatures above 2.4 million degrees Celsius (most stars easily attain this temperature in their interiors), lithium is more abundant than current computations would predict in later-generation stars.

Lithium is also found in brown dwarf substellar objects and certain anomalous orange stars. Because lithium is present in cooler, less-massive brown dwarfs, but is destroyed in hotter red dwarf stars, its presence in the stars' spectra can be used in the "lithium test" to differentiate the two, as both are smaller than the Sun. Certain orange stars can also contain a high concentration of lithium. Those orange stars found to have a higher than usual concentration of lithium (such as Centaurus X-4) orbit massive objects—neutron stars or black holes—whose gravity evidently pulls heavier lithium to the surface of a hydrogen-helium star, causing more lithium to be observed.>>
Art Neuendorffer