APOD: IC 4406: A Seemingly Square Nebula (2017 Jan 08)

[APOD Robot]

IC 4406: A Seemingly Square Nebula

Explanation: How can a round star make a square nebula? This conundrum comes to light when studying planetary nebulae like IC 4406. Evidence indicates that IC 4406 is likely a hollow cylinder, with its square appearance the result of our vantage point in viewing the cylinder from the side. Were IC 4406 viewed from the top, it would likely look similar to the Ring Nebula. This representative-color picture is a composite made by combining images taken by the Hubble Space Telescope in 2001 and 2002. Hot gas flows out the ends of the cylinder, while filaments of dark dust and molecular gas lace the bounding walls. The star primarily responsible for this interstellar sculpture can be found in the planetary nebula's center. In a few million years, the only thing left visible in IC 4406 will be a fading white dwarf star.

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[MarkBour]

Beautiful, delicate image. It reminds me of a cocoon of a silkworm.

The description of IC 4406 in Wikipedia is a bit confusing -- first saying it is a torus shape, then later a prolate spheroid. I suppose it could be the the whole is a prolate spheroid and the most visible part of that is roughly a torus, but that's just an attempt to reconcile the two statements.

[Boomer12k]

It is all a point of view....

Got out the Binocs the other night... below freezing, so only a short while.

:---[===] *

[heehaw]

A striking image!

[JohnD]

Is comparing this with the Ring Nebula correct? If they were so similar, we would see other objects in all possible angular views from straight down the tube (Ring) to a side view (IC4406).
Do we?

John

[NCTom]

Why a tube instead of a sphere? is this related to the magnetic poles of the star?

[neufer]

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Is comparing this with the Ring Nebula correct?

If they were so similar, we would see other objects in all possible angular views from straight down the tube (Ring) to a side view (IC4406).

• Do we?

And where are all the triangular planetary nebula

[Dad is watching]

The kids want to know. If this is a cylindrical object, why is there are there circular appearing areas towards the middle of it instead of 'stripes' around it? Are there two processes at work here?

[Joe25]

Re: Neufer
Try MWC 922: The Red Square Nebula for your triangular planetary nebula answer !
This answers the question of: How can a square nebula form a triangular shape ?

IC 4406 is a tubular structure when viewed from the end of its tube, but here we are viewing it from the side, so it looks somewhat square due the short length of the tube.
M57 the Ring Nebula is a tubular structure and we are viewing it from the end of the tube, thusly it looks round.
M2-9: the Wings of a Butterfly Nebula is also a tube viewed from the side, but it has a well developed Z-Pinch at its central object, whereas IC 4406 has only the very faintest beginnings of a Z-Pinch.
NGC 6751, NGC 3132, NGC 7293, NGC 2392, are also end viewed tubular nebular structures.

In my opinion the label "Planetary Nebula" is technically incorrect, and should be replaced with the correct term "Stellar Z-Pinch Nebula" or SGZ for short.

[geckzilla]

Is comparing this with the Ring Nebula correct? If they were so similar, we would see other objects in all possible angular views from straight down the tube (Ring) to a side view (IC4406).
Do we?

Would you recognize it if you saw it? Nebulas start looking like a jumbled mess when they're not viewed from ideal angles.

[JohnD]

I was almost as lazy, geckzilla.

There are several candidates, easily recognisable, eg Hourglass nebula MyCn18 https://www.spacetelescope.org/images/opo9607a/

John

[Chris Peterson]

Why a tube instead of a sphere? is this related to the magnetic poles of the star?

Or the physical spin axis. Or both in some combination.

[neufer]

Why a tube instead of a sphere? is this related to the magnetic poles of the star?

Or the physical spin axis. Or both in some combination.

• Binary companion stars, planets, accretion disks and polar jets may also play a role.

<<Only about 20% of planetary nebulae are spherically symmetric. A wide variety of shapes exist with some very complex forms seen. Planetary nebulae are classified by different authors into: stellar, disk, ring, irregular, helical, bipolar, quadrupolar, and other types, although the majority of them belong to just three types: spherical, elliptical and bipolar. Bipolar nebulae are concentrated in the galactic plane, likely produced by relatively young massive progenitor stars; and bipolars in the galactic bulge appear to prefer orienting their orbital axes parallel to the galactic plane. On the other hand, spherical nebulae are likely produced by the old stars similar to the Sun.

The huge variety of the shapes is partially the projection effect—the same nebula when viewed under different angles will appear different. Nevertheless, the reason for the huge variety of physical shapes is not fully understood. Gravitational interactions with companion stars if the central stars are binary stars may be one cause. Another possibility is that planets disrupt the flow of material away from the star as the nebula forms. It has been determined that the more massive stars produce more irregularly shaped nebulae. In January 2005, astronomers announced the first detection of magnetic fields around the central stars of two planetary nebulae, and hypothesized that the fields might be partly or wholly responsible for their remarkable shapes.>>

[b][color=#0000FF][size=150]The Cat's Eye Nebula using optical images from the HST and X-ray data from the Chandra X-ray Observatory[/size][/color][/b]

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<<The Cat's Eye Nebula is structurally a very complex nebula, and the mechanism or mechanisms that have given rise to its complicated morphology are not well understood. The central bright part of the nebular consists of the inner elongated bubble (inner ellipse) filled with hot gas. It in turn is nested into a pair of larger spherical bubbles conjoined together along their waist. The waist is observed as the second larger ellipse lying perpendicular to the bubble with hot gas.

The structure of the bright portion of the nebula is primarily caused by the interaction of a fast stellar wind being emitted by the central PNN with the visible material ejected during the formation of the nebula. This interaction causes the emission of X-rays discussed above. The stellar wind, blowing with the velocity as high as 1900 km/s, has 'hollowed out' the inner bubble of the nebula, and appears to have burst the bubble at both ends.

It is also suspected that the central WR:+O7 spectral class PNN star, HD 1064963 / BD +66 1066 / PPM 20679 of the nebula may be generated by a binary star. The existence of an accretion disk caused by mass transfer between the two components of the system may give rise to polar jets, which would interact with previously ejected material. Over time, the direction of the polar jets would vary due to precession.>>

[Chris Peterson]

Why a tube instead of a sphere? is this related to the magnetic poles of the star?

Or the physical spin axis. Or both in some combination.

Binary companion stars, planets, accretion disks and polar jets may also play a role.

True... although that just extends the idea of magnetic and physical spin axes to the entire system, not just a single star. (I'm doubtful that planets play a significant role, except for the rare case of systems where you have a planet and a star of nearly the same mass- and such systems are probably too young for the star to be going through an explosive stage.)

[Ann]

I'm doubtful that planets play a significant role, except for the rare case of systems where you have a planet and a star of nearly the same mass- and such systems are probably too young for the star to be going through an explosive stage.

A planet and a star of nearly the same mass? Isn't that a contradiction in terms?

Ann

[Chris Peterson]

I'm doubtful that planets play a significant role, except for the rare case of systems where you have a planet and a star of nearly the same mass- and such systems are probably too young for the star to be going through an explosive stage.

A planet and a star of nearly the same mass? Isn't that a contradiction in terms?

No, because you could have a binary system where only one component had sufficient mass for fusion to begin. One component that was just barely a star, and one component that just barely wasn't. But the star in that case would be of such low mass that I'd assume it was stable and very long lived- longer than the current age of the Universe.

[geckzilla]

I was almost as lazy, geckzilla.

There are several candidates, easily recognisable, eg Hourglass nebula MyCn18 https://www.spacetelescope.org/images/opo9607a/

I was not lazy. It is unlikely that IC4406 looks anything like MyCn18 from a similar inclination. You might try NGC2346. The reality, however, is that these things are very confusing and it is nearly impossible to discern their true shapes with rare exceptions.

[Cousin Ricky]

Which way is the spin axis? Is it 11 o'clock &ndash; 5 o'clock, or is it 8 o'clock &ndash; 2 o'clock?

[starsurfer]

With yesterday's clue, I was expecting the Red Square Nebula!

[Chris Peterson]

Which way is the spin axis? Is it 11 o'clock &ndash; 5 o'clock, or is it 8 o'clock &ndash; 2 o'clock?

I was thinking the same thing: are we looking at a short stubby cylinder (more like a torus) or a long thin one?

[alter-ego]

Which way is the spin axis? Is it 11 o'clock &ndash; 5 o'clock, or is it 8 o'clock &ndash; 2 o'clock?

I was thinking the same thing: are we looking at a short stubby cylinder (more like a torus) or a long thin one?

Based on the understanding of a 3D M57, I believe the stubby cylinder is the correct view ("spin" axis along 11:00 o'clock - 5:00 o'clock).

[neufer]

I'm doubtful that planets play a significant role, except for the rare case of systems where you have a planet and a star of nearly the same mass- and such systems are probably too young for the star to be going through an explosive stage.

---

<<Bipolar nebulae are concentrated in the galactic plane, likely produced by relatively young massive progenitor stars; and bipolars in the galactic bulge appear to prefer orienting their orbital axes parallel to the galactic plane. On the other hand, spherical nebulae are likely produced by the old stars similar to the Sun.

Another possibility is that [hot Jupiter ] planets disrupt the flow of material away from the star as the nebula forms.>>

[alcor]

As very few planetary nebulae has a square-ish tendency one might say that it is hip to be square amongst these objects. Or just take a listen to http://www.youtube.com/watch?v=LB5YkmjalDg with Huey Lewis And The News playing their song Hip To Be Square.

[Ann]

I'm doubtful that planets play a significant role, except for the rare case of systems where you have a planet and a star of nearly the same mass- and such systems are probably too young for the star to be going through an explosive stage.

A planet and a star of nearly the same mass? Isn't that a contradiction in terms?

No, because you could have a binary system where only one component had sufficient mass for fusion to begin. One component that was just barely a star, and one component that just barely wasn't. But the star in that case would be of such low mass that I'd assume it was stable and very long lived- longer than the current age of the Universe.

Wouldn't the planet then be a brown dwarf? If they are nearly the same mass? Are brown dwarfs really considered planets?

Anyway, a component that is just barely a star can't be much more massive than Proxima Centauri, the tiny M5V star whose mass is about 12% solar. The way I understand it, the projected lifetime of such a tiny star is much longer than the Universe, many, many times the lifetime of the Universe. I think we are talking about trillions of years. And are we really sure that a star like Proxima Centauri will ever produce a planetary nebula? What do we base that understanding on?

Ann

[Chris Peterson]

A planet and a star of nearly the same mass? Isn't that a contradiction in terms?

No, because you could have a binary system where only one component had sufficient mass for fusion to begin. One component that was just barely a star, and one component that just barely wasn't. But the star in that case would be of such low mass that I'd assume it was stable and very long lived- longer than the current age of the Universe.

Wouldn't the planet then be a brown dwarf? If they are nearly the same mass? Are brown dwarfs really considered planets?

Anyway, a component that is just barely a star can't be much more massive than Proxima Centauri, the tiny M5V star whose mass is about 12% solar. The way I understand it, the projected lifetime of such a tiny star is much longer than the Universe, many, many times the lifetime of the Universe. I think we are talking about trillions of years. And are we really sure that a star like Proxima Centauri will ever produce a planetary nebula? What do we base that understanding on?

One man's brown dwarf is another man's planet. In any case, there's less than an order of magnitude in mass between the smallest red dwarf and the largest gas giant (in the form of a sub-brown dwarf). So a fusing and non-fusing pair can be quite close in mass.