by Ann » Sat Oct 05, 2024 7:00 am
I'm not copying the APOD and posting it here, because it is too large! :stamps-foot: It's almost 700 KB.
So I recommend
this thread instead, where you can see a dizzying variety of Dumbbell Nebulas in all the colors of the rainbow! I'm posting two of my favorites here:
So what color is M27
really? Well, planetary nebulas are typically dominated by either cyan-green OIII, whose color is probably something like this,
███, or red hydrogen alpha, which is, well, red,
███. Or, most likely, most planetaries are both OIII-green and Hα-red, like M27.
What makes a star shed its outer layers anyway? It has to do with the pulsations and dust production of the dying red asymptotic giant branch (AGB) star. An AGB star formed from a sunlike progenitor will have an inert core and two shells where fusion is taking place:
So the AGB star has two shells where fusion is taking place, a hydrogen-burning shell and a helium-burning shell. The way I understand it, the hydrogen-burning shell affects the helium-burning shell by dumping more helium on the helium-burning shell. This makes the helium-burning shell fuse in an uneven manner, causing it to pulsate. Also the way I understand it, these pulsations help create dust:
F Dell'Agli et al. wrote:
Asymptotic giant branch (AGB) stars are efficient pollutants of the interstellar medium, because their cool and dense winds prove a favourable environment for dust production. For example, these stars are known to significantly contribute to the chemical enrichment of galaxies as well as up to 40 per cent of interstellar medium dust (e.g. Schneider et al. 2014; Goldman et al. 2022).
The reason why post-AGB stars shed their outer layers is, the way I understand it, the fact that the pulsations create winds that themselves blow away the outer layers of the star's atmosphere, and the extra dust created by the pulsations makes in even easier for the winds to get a good hold on the atmosphere and blow away its dust, taking gas with it.
Of course, once the ultra-hot but cooling inert core has been bared, and its ultra-harsh ultraviolet light is bathing the still nearby gaseous shells and curtains of removed outer stellar atmosphere, then these curtains and shells begin to fluoresce, and we get a planetary nebula.
All right. I don't have much more to say about the AGB stars or the white dwarfs. But I'll say this much. No, M27 is not a comet, but there are many things that are not comets! For example, AGB star Mira, which is shedding its outer layers while at the same time speeding through space, is leaving a 13 light-year-long ultraviolet tail behind it. But it is not a comet.
Also the False Comet in Scorpius is not a comet:
The False Comet in Scorpius.
Credit: Jerry Lodriguss.
And the Comet Galaxy is also not a comet!
Wikipedia wrote about the Comet Galaxy:
This unique spiral galaxy, which is situated 3.2 billion light-years from the Earth, has an extended stream of bright blue knots and diffuse wisps of young stars. It rushes at 3.6 million km/h (1000km/s) through the cluster Abell 2667 and therefore, like a comet, shows a tail, with a length of 600,000 light-years.
Not even comet-like galaxy NGC 4861 is a comet:
So, to summarize,
there are more things that are not comets in Heaven and Earth, Horatio, than are dreamt of in your philosophy. Like 110 Messier objects. And many other things as well.
Ann
I'm not copying the APOD and posting it here, because it is too large! :stamps-foot: It's almost 700 KB.
So I recommend [url=https://www.constellation-guide.com/dumbbell-nebula-messier-27/]this thread[/url] instead, where you can see a dizzying variety of Dumbbell Nebulas in all the colors of the rainbow! I'm posting two of my favorites here:
[float=left][img3="The Dumbbell Nebula, M27. Credit: Göran Nilsson & The Liverpool Telescope (CC BY-SA 4.0)"]https://www.constellation-guide.com/wp-content/uploads/2014/07/Messier-27-Dumbbell-Nebula.webp[/img3][/float][float=right][img3="The Dumbbell Nebula. Credit: Claudio Bottari, Paolo Demaria, Giuseppe Donatiello, Marco Favuzzi, Federico Lavarino, Rolando Ligustri (CAST), Andrea Pistocchini, Bert Scheuneman, Tim Stone, Rubes Turchetti (CAST) (CC0 1.0)"]https://www.constellation-guide.com/wp-content/uploads/2014/07/Dumbbell-Nebula-M27.webp[/img3][/float]
[clear][/clear]
So what color is M27 [b][i]really[/i][/b]? Well, planetary nebulas are typically dominated by either cyan-green OIII, whose color is probably something like this, [color=#4dfed1]███[/color], or red hydrogen alpha, which is, well, red, [color=#FF0000]███[/color]. Or, most likely, most planetaries are both OIII-green and Hα-red, like M27.
What makes a star shed its outer layers anyway? It has to do with the pulsations and dust production of the dying red asymptotic giant branch (AGB) star. An AGB star formed from a sunlike progenitor will have an inert core and two shells where fusion is taking place:
[img3="An AGB star. Credit: I don't know."]https://www.secretsofuniverse.in/wp-content/uploads/2020/05/AGB-star.gif[/img3]
So the AGB star has two shells where fusion is taking place, a hydrogen-burning shell and a helium-burning shell. The way I understand it, the hydrogen-burning shell affects the helium-burning shell by dumping more helium on the helium-burning shell. This makes the helium-burning shell fuse in an uneven manner, causing it to pulsate. Also the way I understand it, these pulsations help create dust:
[quote][url=https://academic.oup.com/mnras/article/526/4/5386/7304421]F Dell'Agli[/url] et al. wrote:
Asymptotic giant branch (AGB) stars are efficient pollutants of the interstellar medium, because their cool and dense winds prove a favourable environment for dust production. For example, these stars are known to significantly contribute to the chemical enrichment of galaxies as well as up to 40 per cent of interstellar medium dust (e.g. Schneider et al. 2014; Goldman et al. 2022).[/quote]
The reason why post-AGB stars shed their outer layers is, the way I understand it, the fact that the pulsations create winds that themselves blow away the outer layers of the star's atmosphere, and the extra dust created by the pulsations makes in even easier for the winds to get a good hold on the atmosphere and blow away its dust, taking gas with it.
Of course, once the ultra-hot but cooling inert core has been bared, and its ultra-harsh ultraviolet light is bathing the still nearby gaseous shells and curtains of removed outer stellar atmosphere, then these curtains and shells begin to fluoresce, and we get a planetary nebula.
[img3="Can you spot M27 in this star field? Oh, I forgot that the image is annotated! Credit: Trinitrix at wikipedia.org"]https://www.constellation-guide.com/wp-content/uploads/2014/07/Dumbbell-Nebula-and-NGC-6830.webp[/img3]
All right. I don't have much more to say about the AGB stars or the white dwarfs. But I'll say this much. No, M27 is not a comet, but there are many things that are not comets! For example, AGB star Mira, which is shedding its outer layers while at the same time speeding through space, is leaving a 13 light-year-long ultraviolet tail behind it. But it is not a comet.
[img3="AGB star Mira is leaving a 13 light-year-long tail behind it as it is speeding through space. Credit: NASA/JPL-Caltech/C. Martin (Caltech)/M. Seibert(OCIW)"]https://upload.wikimedia.org/wikipedia/commons/thumb/9/98/GALEX_Mosaic_of_Mira_A.jpg/1200px-GALEX_Mosaic_of_Mira_A.jpg?20110628182904[/img3]
Also the False Comet in Scorpius is not a comet:
[float=left][img3="The False Comet in Scorpius. The bright white cluster NGC 6231 is the comet's 'head', and the red nebula, IC 4628, is its 'tail'. Note the line of stars connecting NGC 6231 with IC 4628. Credit: Till Credner. "]https://www.allthesky.com/clusters/big/ngc6231-b.jpg[/img3][/float][float=right][attachment=0]Scorpius and the False Comet arrowed Jerry Lodriguss.png[/attachment][c][size=85][color=#0040FF]The False Comet in Scorpius.
Credit: Jerry Lodriguss.[/color][/size][/c][/float]
[clear][/clear]
And the Comet Galaxy is also not a comet!
[img3="The Comet Galaxy is a spiral galaxy located 3.2 billion light-years from Earth, in the galaxy cluster Abell 2667. Credit: NASA - http://www.spacetelescope.org/images/heic0705a/"]https://upload.wikimedia.org/wikipedia/commons/0/0f/CometGalaxy.jpg[/img3]
[quote][url=https://en.wikipedia.org/wiki/Comet_Galaxy]Wikipedia[/url] wrote about the Comet Galaxy:
This unique spiral galaxy, which is situated 3.2 billion light-years from the Earth, has an extended stream of bright blue knots and diffuse wisps of young stars. It rushes at 3.6 million km/h (1000km/s) through the cluster Abell 2667 and therefore, like a comet, shows a tail, with a length of 600,000 light-years.[/quote]
Not even comet-like galaxy NGC 4861 is a comet:
[img3="Comet-like galaxy NGC 4861. Credit: ESA/Hubble"]https://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/NGC_4861_-_HST-_Potw1704a.tif/lossy-page1-1024px-NGC_4861_-_HST-_Potw1704a.tif.jpg[/img3]
So, to summarize, [i]there are more things that are not comets in Heaven and Earth, Horatio, than are dreamt of in your philosophy[/i]. Like 110 Messier objects. And many other things as well. ☄️
Ann