APOD: Jets from the Necklace Nebula (2021 May 18)

[johnnydeep]

I'm frankly surprised they can deduce all that, especially that "The smaller star continued orbiting inside its larger companion, increasing the giant's rotation rate." How could they possible know that? Or is this just a case of this is the ONLY way this ever happens? That is, that when the one star expands at the end of it's life, it will ALWAYS envelop its binary companion, and it will ALWAYS increase the bloated star's rotation rate? Seems unlikely to always be true to me though.

That the system is binary is determined by looking at the periodicity of the light curve, and also at the spectrum, which is consistent with a pair of blackbodies with different temperatures. The conclusion that the stars shared a common envelope before the nebula was ejected (as a circular ring) comes from the very short orbital period (just over a day) and the equatorial ejection pattern.

Ok, thanks. And what about the idea that the orbiting companion increased the giant's rotation rate?

[Chris Peterson]

the order of RGB colors correctly maps the order of wavelenghts of the narrow-band filters:
B 438 nm
OIII 502 nm
V 555 nm
I 814 nm
H-alpha 656 nm
NII 658 nm

Note that the B, V, and I filters are all broadband. An image made with just these three would approximate "true" colors, with some distortion due to the red channel being pushed to longer wavelengths than we can see, and having poor overlap with the green channel. The addition of the narrowband filters adds more color distortion, although probably not too severe since, as you point out, these narrow bands are mapped into the output color channels where we would expect to find them.

Technically, the use of the IR filter means that this image is described as "false-color". But probably not so far from "true color" to make Ann too unhappy!

Hmm. I haven't commented on this APOD, except to express my delight over the cute kitties that were hidden in one of the links, and that Orin "unearthed" for me!

The reason why I haven't commented on the Necklace Nebula is precisely because I don't trust the colors. Yes, I can imagine that the green stuff in the center of the nebula is green OIII, and the pink "flares" emerging from the "necklace" itself might be Hα, possibly mixed with something to make it look diluted.

But what is all the blue stuff? And why is it blue? The way I understand it, planetary nebulas are not typically blue at all. And I hate it when non-blue objects are shown as blue, because it makes me so disappointed to find out that they are really non-blue. For example, I once read about a certain kind of white dwarfs (helium-rich white dwarfs, I think), that turned blue when they grew colder. I thought that was really neat.

Yes, but then I read about what really happened to these white dwarfs! At a certain temperature, when the white dwarfs had grown so cold that they emitted most of their light in the infrared part of the spectrum, their emission shifted from invisible infrared to visible red! So these stars grew bluer by growing redder!!!

(Yes, I know, I know - the wavelengths of visible red light are shorter than the wavelengths of infrared light. So instead of emitting photons of increasingly large wavelengths, these cooling helium-rich dwarfs suddenly "jumped backwards" and emitted light of a shorter wavelength, namely red! Therefore these optically redder white dwarfs could be described as growing bluer! I understand the reasoning, but I hated it!)

So, in short, Chris, does the Necklace Nebula really emit a lot of truly blue light, or should I ignore this nebula the way I ignore those "blue but red" helium white dwarfs?

Ann

This white dwarf is only a few thousand years old. It has to be so hot that most of its output in in the UV. So in the context of the filters used, it is blue. The apparent blue of the nebula is, perhaps, a mix of reflected light from the central stars and emissions from oxygen (which the wideband blue filter will capture). The choice of color mapping is consistent with an approximation of true colors, but there is more to it than that, since we know nothing about the weighting of each channel in the final processing.

[Chris Peterson]

I'm frankly surprised they can deduce all that, especially that "The smaller star continued orbiting inside its larger companion, increasing the giant's rotation rate." How could they possible know that? Or is this just a case of this is the ONLY way this ever happens? That is, that when the one star expands at the end of it's life, it will ALWAYS envelop its binary companion, and it will ALWAYS increase the bloated star's rotation rate? Seems unlikely to always be true to me though.

That the system is binary is determined by looking at the periodicity of the light curve, and also at the spectrum, which is consistent with a pair of blackbodies with different temperatures. The conclusion that the stars shared a common envelope before the nebula was ejected (as a circular ring) comes from the very short orbital period (just over a day) and the equatorial ejection pattern.

Ok, thanks. And what about the idea that the orbiting companion increased the giant's rotation rate?

I don't know for sure, but I'd assume that's an inevitable consequence of merged stellar envelopes, based on theory and modeling.

[johnnydeep]

That the system is binary is determined by looking at the periodicity of the light curve, and also at the spectrum, which is consistent with a pair of blackbodies with different temperatures. The conclusion that the stars shared a common envelope before the nebula was ejected (as a circular ring) comes from the very short orbital period (just over a day) and the equatorial ejection pattern.

Ok, thanks. And what about the idea that the orbiting companion increased the giant's rotation rate?

I don't know for sure, but I'd assume that's an inevitable consequence of merged stellar envelopes, based on theory and modeling.

Ok. I can accept that

[VictorBorun]

I don't see anything I'd describe unambiguously as shadows, and certainly not "harsh" ones.

They must be radial wind shadows, glowing rather than glooming

Click to view full size image

By the way, it's a way to decorate the face of a wristwatch: "Perfect reproduction of the most beautiful Nebula is ever On Time"

[johnnydeep]

I don't see anything I'd describe unambiguously as shadows, and certainly not "harsh" ones.

They must be radial wind shadows, glowing rather than glooming

Click to view full size image

By the way, it's a way to decorate the face of a wristwatch: "Perfect reproduction of the most beautiful Nebula is ever On Time"

Now THAT would indeed be pretty darn cool to have! Perhaps if Apple introduced a round version of the Apple Watch it could be a custom option

[VictorBorun]

The jewels in the Necklace Nebula are asumed to be some clumps in the giant star's equatorial part that broke apart from the giant star when its rotation was accelerated beacause of the dwarf star companion sinking into the giant star.

Now we are familiar with some clumps in Sun's convection zone: there a few magnetic whirls that suface every 11 years and can be seen as pairs of spots. Can similar whirls in a giant star be rigid enough to survive the ripping of the equator?

By the way, can the Sun's spots be traced from one solar cycle to the next?

[Ann]

The pearly clumps of the Necklace Nebula might be cometary knots.

The Helix Nebula with cometary knots along the perimeter of its 'dust ring'. Photo: NASA, ESA, and C.R. O'Dell (Vanderbilt University)

---

Closeup of some cometary knots in the Helix Nebula. NASA, Hubble, C. Robert O'Dell and Kerry P. Handron (Rice University).

---

Consider the Helix Nebula, a large and relatively old planetary nebula. There is a rarefied inner "hole" in the Helix Nebula, surrounded by a ring (or a cylinder?) of denser gas and dust. Along the perimeter of this ring (let's call it a ring), there are cometary knots, which are slightly similar to dust pillars in sites of high-mass star formation.

That's why I'm wondering if the pearls in the Necklace Nebula may be the "heads" of cometary knots in this nebula.

Ann

[MarkBour]

That's why I'm wondering if the pearls in the Necklace Nebula may be the "heads" of cometary knots in this nebula.

Ann

That sounds right to me.
https://en.wikipedia.org/wiki/Post_comm ... ope_binary

[Chris Peterson]

The pearly clumps of the Necklace Nebula might be cometary knots.

They don't look like it to me. The dense regions are very unstructured, the tails are broad, and the overall size seems much too great. It is interesting to speculate on whether these structures might be progenitors to cometary knots, though.

[Chris Peterson]

The jewels in the Necklace Nebula are asumed to be some clumps in the giant star's equatorial part that broke apart from the giant star when its rotation was accelerated beacause of the dwarf star companion sinking into the giant star.

Now we are familiar with some clumps in Sun's convection zone: there a few magentic whirls that suface every 11 years and can be seen as pairs of spots. Can similar whirls in a giant star be rigid enough to survive the ripping of the equator?

By the way, can the Sun's spots be traced from one solar cycle to the next?

Sunspots are unrelated to any static structure in the Sun. They form and they dissolve. They can't even be traced for more than a solar rotation or two, let alone for years. It's like asking if a cloud can be traced from year to year.

[johnnydeep]

The jewels in the Necklace Nebula are asumed to be some clumps in the giant star's equatorial part that broke apart from the giant star when its rotation was accelerated beacause of the dwarf star companion sinking into the giant star.

Now we are familiar with some clumps in Sun's convection zone: there a few magentic whirls that suface every 11 years and can be seen as pairs of spots. Can similar whirls in a giant star be rigid enough to survive the ripping of the equator?

By the way, can the Sun's spots be traced from one solar cycle to the next?

Sunspots are unrelated to any static structure in the Sun. They form and they dissolve. They can't even be traced for more than a solar rotation or two, let alone for years. It's like asking if a cloud can be traced from year to year.

Then there's the Great Red Spot on Jupiter, which has persisted for hundreds of years. So, at least some atmospheric phenomena can be very stable and long lived, provide the atmosphere has the appropriate constituents and dynamics

[Chris Peterson]

The jewels in the Necklace Nebula are asumed to be some clumps in the giant star's equatorial part that broke apart from the giant star when its rotation was accelerated beacause of the dwarf star companion sinking into the giant star.

Now we are familiar with some clumps in Sun's convection zone: there a few magentic whirls that suface every 11 years and can be seen as pairs of spots. Can similar whirls in a giant star be rigid enough to survive the ripping of the equator?

By the way, can the Sun's spots be traced from one solar cycle to the next?

Sunspots are unrelated to any static structure in the Sun. They form and they dissolve. They can't even be traced for more than a solar rotation or two, let alone for years. It's like asking if a cloud can be traced from year to year.

Then there's the Great Red Spot on Jupiter, which has persisted for hundreds of years. So, at least some atmospheric phenomena can be very stable and long lived, provide the atmosphere has the appropriate constituents and dynamics :)

Of course, "long lived" is a very subjective concept, heavily biased by human experience.

[neufer]

Sunspots are unrelated to any static structure in the Sun. They form and they dissolve. They can't even be traced for more than a solar rotation or two, let alone for years. It's like asking if a cloud can be traced from year to year.

Then there's the Great Red Spot on Jupiter, which has persisted for hundreds of years. So, at least some atmospheric phenomena can be very stable and long lived, provide the atmosphere has the appropriate constituents and dynamics

Of course, "long lived" is a very subjective concept, heavily biased by human experience.

• Or by other anticyclonic storms:

The Great Dark Spot as seen from Voyager 2

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<<The Great Dark Spot was one of a series of dark spots on Neptune similar in appearance to Jupiter's Great Red Spot. Like Jupiter's spot, Great Dark Spots are anticyclonic storms. However, their interiors are relatively cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be shorter, forming and dissipating once every few years or so. Based on observations taken with Voyager 2 and since then with the Hubble Space Telescope, Neptune appears to spend somewhat more than half its time with a Great Dark Spot.

The dark, elliptically-shaped spot (with initial dimensions of 13,000 × 6,600 km) of GDS-89 was about the same size as Earth, and was similar in general appearance to Jupiter's Great Red Spot. Around the edges of the storm, winds were measured at up to 2,100 kilometers per hour, the fastest recorded in the Solar System. The Great Dark Spot is thought to be a hole in the methane cloud deck of Neptune. The spot was observed at different times with different sizes and shapes.

In 1989, GDS-89 was the first Great Dark Spot on Neptune to be observed by NASA's Voyager 2 spaceprobe. When the spot was to be photographed again in November 1994 by the Hubble Space Telescope, it had disappeared completely, leaving astronomers to believe that it has either been covered up or vanished. The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer visible as a dark feature. Dark spots may dissipate when they migrate too close to the equator, or possibly through some other unknown mechanisms.

However, in 2016, an almost identical spot emerged in Neptune's northern hemisphere. This new spot, called the Great Dark Spot (NGDS), has remained visible for several years. It is unknown whether this spot is still present on the planet, as observations using the Hubble telescope are limited. More recently, in 2018, a newer main dark spot and smaller dark spot were identified and studied. In August 2020, the new Great Dark Spot suddenly stopped its southward motion and reversed direction, contrary to projections that the storm would continue to the equator, where it would have met its likely demise. Around the same time, a smaller "Dark Spot Jr." was found near the larger storm, before disappearing later on. This led astronomers to believe that the storm's reversal of motion may have been related to the birth of the smaller storm.>>

[VictorBorun]

The pearly clumps of the Necklace Nebula might be cometary knots.

The Helix Nebula with cometary knots along the perimeter of its 'dust ring'. Photo: NASA, ESA, and C.R. O'Dell (Vanderbilt University)

---

Closeup of some cometary knots in the Helix Nebula. NASA, Hubble, C. Robert O'Dell and Kerry P. Handron (Rice University).

---

Consider the Helix Nebula, a large and relatively old planetary nebula. There is a rarefied inner "hole" in the Helix Nebula, surrounded by a ring (or a cylinder?) of denser gas and dust. Along the perimeter of this ring (let's call it a ring), there are cometary knots, which are slightly similar to dust pillars in sites of high-mass star formation.

That's why I'm wondering if the pearls in the Necklace Nebula may be the "heads" of cometary knots in this nebula.

Ann

Well, a comet's tail takes matter from the comet and energy from the stellar wind and looks like glowing wind shadow, right?
The Helix Nebula is a star's equatorial shell, just like the Necklace Nebula; so I must ask the same question:

is the ring (or helix coil) of jewels with glowing outward-radial wind-shadows in fact a ring of what had become now of magnetic whirls in the equator band of a giant star's surface at the moment when the rotation accelerated and the equator blew off?
I mean magnetic whirls similar to pairs of dark spots that surface in the Sun after passing all the way through Sun's convection layer.
Then those clumps are not just some ealier dust at the circular leading edge of the explosion; they are newborn dust from the star's outer layer?

[Puddock]

Thanks neufer!

[Chris Peterson]

Well, a comet's tail takes matter from the comet and energy from the stellar wind and looks like glowing wind shadow, right?

I don't know what a "wind shadow" is. But a comet's tails are the result of gas and dust evaporated from a solid surface, with the dust tail shaped by a combination of solar wind and orbital dynamics, and a gas tail shaped by photon pressure. The only thing that comets and cometary knots have in common are five letters from the alphabet.

is the ring (or helix coil) of jewels with glowing outward-radial wind-shadows in fact a ring of what had become now of magnetic whirls in the equator band of a giant star's surface at the moment when the rotation accelerated and the equator blew off?
I mean magnetic whirls similar to pairs of dark spots that surface in the Sun after passing all the way through Sun's convection layer.
Then those clumps are not just some ealier dust at the circular leading edge of the explosion; they are newborn dust from the star's outer layer?

The clumps are mainly gas, not dust. The structure in planetary nebulas is determined by many things, and stellar magnetic fields at the time the outer atmosphere is ejected may be one of them.

[Ann]

Well, a comet's tail takes matter from the comet and energy from the stellar wind and looks like glowing wind shadow, right?

I don't know what a "wind shadow" is. But a comet's tails are the result of gas and dust evaporated from a solid surface, with the dust tail shaped by a combination of solar wind and orbital dynamics, and a gas tail shaped by photon pressure. The only thing that comets and cometary knots have in common are five letters from the alphabet.

is the ring (or helix coil) of jewels with glowing outward-radial wind-shadows in fact a ring of what had become now of magnetic whirls in the equator band of a giant star's surface at the moment when the rotation accelerated and the equator blew off?
I mean magnetic whirls similar to pairs of dark spots that surface in the Sun after passing all the way through Sun's convection layer.
Then those clumps are not just some ealier dust at the circular leading edge of the explosion; they are newborn dust from the star's outer layer?

The clumps are mainly gas, not dust. The structure in planetary nebulas is determined by many things, and stellar magnetic fields at the time the outer atmosphere is ejected may be one of them.

The central star of the Necklace Nebula used to be a terminally pulsating Asymtotic Giant Branch (AGB) star. This is the terminal phase of ordinary medium-mass stars (1-8 M_☉), before they shut off fusion, cast off their outer atmospheres and become planetary nebulas and white dwarfs.

During their terminally pulsating phase, AGB stars have a "dead core" surrounded by a helium shell and a hydrogen shell, which support the star through helium and hydrogen fusion. The two shells are "synchronized" in a sort of feedback loop, and "switch on" and "switch off" alternatively, as the helium shell is either thick enough or too thin to support helium fusion, and the hydrogen shell is either hot enough or too cool to fuse hydrogen. This "off and on" fusion makes the star unstable and helps drive increased mass loss.

AGB star Mira with its extremely long tail, which is probably caused by Mira's mass loss as the star speeds through the interstellar medium. NASA - http://www.galex.caltech.edu/MEDIA/2007-04/images.html

---

Not only do AGB stars lose a lot of mass, but they produce a lot of dust, too.

Wikipedia wrote:

The stellar winds from AGB stars are sites of cosmic dust formation, and are believed to be the main production sites of dust in the universe.

The Necklace Nebula. ESA, Hubble, NASA; Processing: K. Noll

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Hubble palette image of young star cluster and nebula M16.

---

Aren't there some similarities between the Necklace Nebula and star forming region M16? We have the presence of a very hot star or stars, a rarefied inner nebula and a dusty perimeter decorated with dusty protrusions, all pointing inward toward the hot stars.

I'm not suggesting that planetary nebulas and young sites of star formation are the same, or function in the same way. Of course not. But there might be some similarities.

Ann

[Chris Peterson]

Well, a comet's tail takes matter from the comet and energy from the stellar wind and looks like glowing wind shadow, right?

I don't know what a "wind shadow" is. But a comet's tails are the result of gas and dust evaporated from a solid surface, with the dust tail shaped by a combination of solar wind and orbital dynamics, and a gas tail shaped by photon pressure. The only thing that comets and cometary knots have in common are five letters from the alphabet.

is the ring (or helix coil) of jewels with glowing outward-radial wind-shadows in fact a ring of what had become now of magnetic whirls in the equator band of a giant star's surface at the moment when the rotation accelerated and the equator blew off?
I mean magnetic whirls similar to pairs of dark spots that surface in the Sun after passing all the way through Sun's convection layer.
Then those clumps are not just some ealier dust at the circular leading edge of the explosion; they are newborn dust from the star's outer layer?

The clumps are mainly gas, not dust. The structure in planetary nebulas is determined by many things, and stellar magnetic fields at the time the outer atmosphere is ejected may be one of them.

The central star of the Necklace Nebula used to be a terminally pulsating Asymtotic Giant Branch (AGB) star. This is the terminal phase of ordinary medium-mass stars (1-8 M_☉), before they shut off fusion, cast off their outer atmospheres and become planetary nebulas and white dwarfs.

During their terminally pulsating phase, AGB stars have a "dead core" surrounded by a helium shell and a hydrogen shell, which support the star through helium and hydrogen fusion. The two shells are "synchronized" in a sort of feedback loop, and "switch on" and "switch off" alternatively, as the helium shell is either thick enough or too thin to support helium fusion, and the hydrogen shell is either hot enough or too cool to fuse hydrogen. This "off and on" fusion makes the star unstable and helps drive increased mass loss.

AGB star Mira with its extremely long tail, which is probably caused by Mira's mass loss as the star speeds through the interstellar medium. NASA - http://www.galex.caltech.edu/MEDIA/2007-04/images.html

---

Not only do AGB stars lose a lot of mass, but they produce a lot of dust, too.

Wikipedia wrote:

The stellar winds from AGB stars are sites of cosmic dust formation, and are believed to be the main production sites of dust in the universe.

The Necklace Nebula. ESA, Hubble, NASA; Processing: K. Noll

---

Hubble palette image of young star cluster and nebula M16.

---

Aren't there some similarities between the Necklace Nebula and star forming region M16? We have the presence of a very hot star or stars, a rarefied inner nebula and a dusty perimeter decorated with dusty protrusions, all pointing inward toward the hot stars.

I'm not suggesting that planetary nebulas and young sites of star formation are the same, or function in the same way. Of course not. But there might be some similarities.

Ann

Keep in mind that highly dusty nebulas are from 1-2% dust, by mass. The rest is gas.

[Ann]

Keep in mind that highly dusty nebulas are from 1-2% dust, by mass. The rest is gas.

Of course, Chris. But that's not really the point, is it?

The point is that there is a lot more dust in the dense-looking structures than in the rarefied inner parts of planetary nebulas. There is more gas there too, yes. But there is more dust. And the reason why we see elongated structures like pillars near hot stars in young clusters, and cometary knots with tails in older planetary nebulas like the Helix, is precisely because the "head" of the pillar or the cometary knot shields the parts directly below it from the scorching ultraviolet light from the young stars or from the white dwarf.

Surely it is the dust in the tops of these denser-than-average structures that does most of the shielding of the structures below them from the harsh radiation that would otherwise destroy them?

Doesn't the dust in the Milky Way shield us from some of the goings-on near the center of our galaxy?

Ann

[Chris Peterson]

Keep in mind that highly dusty nebulas are from 1-2% dust, by mass. The rest is gas.

Of course, Chris. But that's not really the point, is it?

The point is that there is a lot more dust in the dense-looking structures than in the rarefied inner parts of planetary nebulas. There is more gas there too, yes. But there is more dust. And the reason why we see elongated structures like pillars near hot stars in young clusters, and cometary knots with tails in older planetary nebulas like the Helix, is precisely because the "head" of the pillar or the cometary knot shields the parts directly below it from the scorching ultraviolet light from the young stars or from the white dwarf.

I'm not convinced that the two kinds of structures are analogous or form in similar ways.

Surely it is the dust in the tops of these denser-than-average structures that does most of the shielding of the structures below them from the harsh radiation that would otherwise destroy them?

Don't call me Shirley!

Doesn't the dust in the Milky Way shield us from some of the goings-on near the center of our galaxy?

Shield in what way? It certainly blocks some visible light from passing through. What other physical consequences do you suggest?

[Ann]

Don't call me Shirley!

Ignorant Swede ¯\_(ツ)_/¯

Ann

[VictorBorun]

Doesn't the dust in the Milky Way shield us from some of the goings-on near the center of our galaxy?

Shield in what way? It certainly blocks some visible light from passing through. What other physical consequences do you suggest?

What if the core bulge of the Milky Way, or any bar, or the supermassive black hole send our way some high energy harmful cosmic rays, but the gas-dust disk blocks it?

[Chris Peterson]

Shield in what way? It certainly blocks some visible light from passing through. What other physical consequences do you suggest?

What if the core bulge of the Milky Way, or any bar, or the supermassive black hole send our way some high energy harmful cosmic rays, but the gas-dust disk blocks it?

I don't think light years of thin dust has much effect on cosmic rays. Or that we are close enough to anything going on at the galaxy center for it to have much effect on us.

[VictorBorun]

Shield in what way? It certainly blocks some visible light from passing through. What other physical consequences do you suggest?

What if the core bulge of the Milky Way, or any bar, or the supermassive black hole send our way some high energy harmful cosmic rays, but the gas-dust disk blocks it?

I don't think light years of thin dust has much effect on cosmic rays. Or that we are close enough to anything going on at the galaxy center for it to have much effect on us.

Let me think.
The total thickness of dust material is probably enough to block some visible light (though most of the visible light can well be absorbed or scattered by neutral gas in the thin disk). But an X ray photon not to mention a gamma ray photon need much more blocking than a solid substance layer which is just few dust particles thick.
Yes, the dust and neutral gas of the disk just block our view of the galactic core and do not do much of a protection against any high energy bursts.