APOD: The Extraordinary Spiral in LL Pegasi (2018 Jul 08)

[APOD Robot]

The Extraordinary Spiral in LL Pegasi

Explanation: What created the strange spiral structure on the upper left? No one is sure, although it is likely related to a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected. The huge spiral spans about a third of a light year across and, winding four or five complete turns, has a regularity that is without precedent. Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The star system that created it is most commonly known as LL Pegasi, but also AFGL 3068. The unusual structure itself has been cataloged as IRAS 23166+1655. The featured image was taken in near-infrared light by the Hubble Space Telescope. Why the spiral glows is itself a mystery, with a leading hypothesis being illumination by light reflected from nearby stars.

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[Ann]

This picture has been an APOD before, which is certainly fine since Sunday is repeat day. The picture itself is so remarkable that it really deserves to be the APOD more than once.

I googled "LL Pegasi" and got the coordinates of the amazing spiral, 23 19 12.607 +17 11 33.13. That way I could use my software Guide to look it up, really only to try to find out what kind of star is seen next to it in the picture. If I got the coordinates right - and I was only able to fill in 23 19 13 and +17 11 33 - then the star is a tiny little 12th magnitude thing whose designation is given by Guide as 3UC215-331878.

The only color information on the star provided by Guide is that its J-K index is 0.54. To the best of my shaky understanding, this makes 3UC215-331878 a somewhat but not tremendously red star, perhaps one of those K0III stars which are a dime a dozen. If 3UC215-331878 is a K0III star, then its true luminosity may be anything from, oh, 30 times the Sun in visual light to perhaps 300 times the Sun. On the other hand, 3UC215-331878 might also be a main sequence K0V star, in which case it is at best half as bright as the Sun and much closer to us than if it is an evolved giant. Whatever!

In any case, if that brilliant star in the picture is only 12th magnitude, then we can only begin to imagine how faint the amazing spiral is.

Click to view full size image

White dwarf spectrum.
Source: https://archive.stsci.edu/prepds/wd-linelist/

What I find very strange and completely remarkable is that the center of the spiral, which ought to be the power source of this amazing pinwheel, is dark, unlike the glowing spiral. Moreover, since today's APOD is a near infrared image, the central source should show up even if it was somewhat shrouded in dust.

Is it possible that the source could be too hot to show up much in a near-infrared image? Perhaps if the central source is a white dwarf (or a binary pair of white dwarfs)?

If you check out the white dwarf spectrum at left, you can see that it peaks in the far ultraviolet. 1000 Å (or 100 nm) is the far ultraviolet part of the spectrum, and 3000 Å is, unless I'm wrong, the near ultraviolet part of it. 3000 Å is not even visible as dark purple to most people, and it is very far from the infrared part of the spectrum. So if there is a white dwarf (or a binary white dwarf) at the center of the spiral, and if the harsh ultraviolet light from them has blasted the nearby dust particles to smithereens, then maybe there is a luminous source at the center which, however, is too hot to show up in this picture.

Is that possible?

Or is it more likely that the central source is so heavily shrouded in dust that it looks dark even at near infrared wavelengths?

Ann

[heehaw]

Clearly a star to wish upon! (and who is Sagain?)

[ck1]

This effect is caused by a black hole with a weak gravitational pull so far not seen nor understood. As gasses enter the black hole a force inside with a more powerful force than the gravitational pull expels the gasses back out into space with the same effect as a smoker blowing out the smoke from his mouth with his lips formed to create a circle.

[neufer]

Click to play embedded YouTube video.

Click to play embedded YouTube video.

[Picky APOD Fan]

Type the last syllable of the word that does not belong. leavitt, einstein, sagain, galileo, copernicus, hubble, wombat, newton:

I thought it was a trick question. Shouldn't "gain" be a correct answer too?

Thanks for an actual deep sky repeat instead of another landscape or cloud pic.

[Bob]

Interesting that is it not a Fibonacci sequence. Perhaps because of regional gravitational effects?

[heehaw]

Type the last syllable of the word that does not belong. leavitt, einstein, sagain, galileo, copernicus, hubble, wombat, newton:
Shouldn't "gain" be a correct answer too?

I believe it is a typo for Carl Sagan!

[bystander]

This picture has been an APOD before, which is certainly fine since Sunday is repeat day. The picture itself is so remarkable that it really deserves to be the APOD more than once.

It was actually this image that was featured twice, in 2016 and 2010. LL Pegasi was also featured in studies using ALMA in 2012 and 2017.

[sunson]

The Extraordinary Spiral in LL Pegasi

Explanation: "Why the spiral glows is itself a mystery, with a leading hypothesis being illumination by light reflected from nearby stars."

1- since the spiral is evenly illuminated, the stars would have to be evenly distributed around the spiral. According to me...unlike it.
2- the stars would show more bright than the spiral itself. They are not.

so, probably is some other cause for the brightness of the spiral.

[neufer]

Interesting that is it not a Fibonacci sequence. Perhaps because of regional gravitational effects?

• It is an Archimedean spiral not a (Fibonacci related) logarithmic spiral:

Archimedean spiral

---

(Fibonacci related) logarithmic spiral

---

The Archimedean spiral has the property that any ray from the origin intersects successive turnings of the spiral in points with a constant separation distance, hence the name "arithmetic spiral". The spiral corresponds to the locations over time of a point moving away from a fixed point with a constant speed along a line which rotates with constant angular velocity. In contrast to this, in a logarithmic spiral these distances, as well as the distances of the intersection points measured from the origin, form a geometric progression.

One method of squaring the circle, due to Archimedes, makes use of an Archimedean spiral. Archimedes also showed how the spiral can be used to trisect an angle. Both approaches relax the traditional limitation on the use of straightedge and compass.

The Archimedean spiral has a variety of real-world applications. Scroll compressors, made from two interleaved involutes of a circle of the same size that almost resemble Archimedean spirals, are used for compressing gases. The coils of watch balance springs and the grooves of very early gramophone records form Archimedean spirals, making the grooves evenly spaced (although variable track spacing was later introduced to maximize the amount of music that could be cut onto a record). Asking for a patient to draw an Archimedean spiral is a way of quantifying human tremor; this information helps in diagnosing neurological diseases. Archimedean spirals are also used in digital light processing (DLP) projection systems to minimize the "rainbow effect", making it look as if multiple colors are displayed at the same time, when in reality red, green, and blue are being cycled extremely quickly. Additionally, Archimedean spirals are used in food microbiology to quantify bacterial concentration through a spiral platter. They are also used to model the pattern that occurs in a roll of paper or tape of constant thickness wrapped around a cylinder.

[Chris Peterson]

Explanation: "Why the spiral glows is itself a mystery, with a leading hypothesis being illumination by light reflected from nearby stars."

1- since the spiral is evenly illuminated, the stars would have to be evenly distributed around the spiral. According to me...unlike it.
2- the stars would show more bright than the spiral itself. They are not.

so, probably is some other cause for the brightness of the spiral.

The size of the spiral is small in comparison to the distance to nearby stars. So any individual star (or group of stars) will evenly illuminate all of the spiral. And at the scale of the image, nearby stars are outside the frame.

[scr33d]

The APOD explanation makes this object more mysterious than it is. Much is known about it:

https://alma-telescope.jp/en/news/mt-an ... th_a_twist

and the Nature article:

https://www.nature.com/articles/s41550-017-0060

[ta152h0]

And this image in not a painting... Need another ice cold one

[neufer]

The APOD explanation makes this object more mysterious than it is. Much is known about it:

The composite image of molecular gas around an old star LL Pegasi. Credit: ALMA(ESO/NAOJ/NRAO), Hyosun Kim et al.

---

<<The regularity of the pattern was quite surprising, leading to its being considered as a binary system in a circular orbit. It is now equally striking that this best-characterized, unambiguous, and complete spiral is actually influenced by an elliptical-orbit binary.

“While the HST image shows us the beautiful spiral structure, it is a 2D projection of a 3D shape, which becomes fully revealed in the ALMA data,” says Raghvendra Sahai (JPL, USA), a co-author of the study. The new ALMA images reveal the spatio-kinematic information of dense molecular gas in the spiral-shell pattern, unveiling the dynamics of the mass loss from the giant star modulated by its orbital motion.

The new ALMA images reveal the detailed features of spiral-shell pattern imprinted in the gas material continuously ejected from LL Pegasi. A comparison of this observation with computer simulations led the team, for the first time, to the conclusion that a highly elliptical orbit is responsible for the morphology of gas distribution surrounding this binary system. In particular, the bifurcation of the spiral-shell pattern that is clearly visible in the ALMA images, is a unique characteristic of elliptical binaries. This quintessential object opens a new window on the nature of central binaries through the recurrent patterns that reside far from the star at distances of a few thousand the stellar radii.>>

---

<<A scroll compressor (also called spiral compressor, scroll pump and scroll vacuum pump) is a device for compressing air or refrigerant. It is used in air conditioning equipment, as an automobile supercharger (where it is known as a scroll-type supercharger) and as a vacuum pump. Many residential central heat pump and air conditioning systems and a few automotive air conditioning systems employ a scroll compressor instead of the more traditional rotary, reciprocating, and wobble-plate compressors. A scroll compressor operating in reverse is known as a scroll expander, and can be used to generate mechanical work from the expansion of a fluid, compressed air or gas.>>

[Ann]

The APOD explanation makes this object more mysterious than it is. Much is known about it:

The composite image of molecular gas around an old star LL Pegasi. Credit: ALMA(ESO/NAOJ/NRAO), Hyosun Kim et al.

---

<<The regularity of the pattern was quite surprising, leading to its being considered as a binary system in a circular orbit. It is now equally striking that this best-characterized, unambiguous, and complete spiral is actually influenced by an elliptical-orbit binary.

“While the HST image shows us the beautiful spiral structure, it is a 2D projection of a 3D shape, which becomes fully revealed in the ALMA data,” says Raghvendra Sahai (JPL, USA), a co-author of the study. The new ALMA images reveal the spatio-kinematic information of dense molecular gas in the spiral-shell pattern, unveiling the dynamics of the mass loss from the giant star modulated by its orbital motion.

The new ALMA images reveal the detailed features of spiral-shell pattern imprinted in the gas material continuously ejected from LL Pegasi. A comparison of this observation with computer simulations led the team, for the first time, to the conclusion that a highly elliptical orbit is responsible for the morphology of gas distribution surrounding this binary system. In particular, the bifurcation of the spiral-shell pattern that is clearly visible in the ALMA images, is a unique characteristic of elliptical binaries. This quintessential object opens a new window on the nature of central binaries through the recurrent patterns that reside far from the star at distances of a few thousand the stellar radii.>>

The picture you posted shows a bright center inside the spiral, but in today's APOD the center is dark. So maybe the dark center of the spiral in today's APOD is just a processing quirk, then?

Ann

[Chris Peterson]

The picture you posted shows a bright center inside the spiral, but in today's APOD the center is dark. So maybe the dark center of the spiral in today's APOD is just a processing quirk, then?

The ALMA image is constructed from submillimeter radio waves- around a thousand times the wavelength of the IR imagery in today's APOD. It's hardly surprising that things look quite different between the two images, outside the basic spiral structure itself.

[neufer]

The picture you posted shows a bright center inside the spiral, but in today's APOD the center is dark. So maybe the dark center of the spiral in today's APOD is just a processing quirk, then?

The ALMA image is constructed from submillimeter radio waves- around a thousand times the wavelength of the IR imagery in today's APOD. It's hardly surprising that things look quite different between the two images, outside the basic spiral structure itself.

• The loveliest girl in Vienna
  Was ALMA, the smartest as well,
  Once she picked you up on by antenna,
  You'd never be free of her spell.

[Boomer12k]

It reminds me of a spinning water balloon, with a LEAK... you throw it into the air, spinning, and the water leaks in a spiral...

Or a spinning smoke bomb on the 4th of July.... the gas spirals outward...

:---[===] *

[Ann]

The picture you posted shows a bright center inside the spiral, but in today's APOD the center is dark. So maybe the dark center of the spiral in today's APOD is just a processing quirk, then?

The ALMA image is constructed from submillimeter radio waves- around a thousand times the wavelength of the IR imagery in today's APOD. It's hardly surprising that things look quite different between the two images, outside the basic spiral structure itself.

Thanks, Chris. Of course, that still doesn't explain the extraordinary fact that the center of the spiral looks dark in the near-infrared image of the APOD.

Ann

[geckzilla]

Type the last syllable of the word that does not belong. leavitt, einstein, sagain, galileo, copernicus, hubble, wombat, newton:
Shouldn't "gain" be a correct answer too?

I believe it is a typo for Carl Sagan!

That it is. Thanks for pointing it out. It is fixed now. (Spammers make me weary.)

[Chris Peterson]

The picture you posted shows a bright center inside the spiral, but in today's APOD the center is dark. So maybe the dark center of the spiral in today's APOD is just a processing quirk, then?

The ALMA image is constructed from submillimeter radio waves- around a thousand times the wavelength of the IR imagery in today's APOD. It's hardly surprising that things look quite different between the two images, outside the basic spiral structure itself.

Thanks, Chris. Of course, that still doesn't explain the extraordinary fact that the center of the spiral looks dark in the near-infrared image of the APOD.

Well, I'd simply say that it's telling us that the entire structure is emissive in submillimeter radio waves, but there is very little near IR emission, only reflection, so in that band the stars don't show up.