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

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Expand view Topic review: APOD: IC 4406: A Seemingly Square Nebula (2017 Jan 08)

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

by Chris Peterson » Sat Jan 14, 2017 3:40 pm

Cousin Ricky wrote:
Chris Peterson wrote:
Cousin Ricky wrote: Shouldn't that be liquids and solids?
I used "fluids" deliberately, since gases, liquids, and solids are all capable of existing as fluids, and it is the fluid properties that allow something to act (at least to some degree) as a rigid, semi-rigid, or otherwise cohesive body, as opposed to a tenuous gas.
You didn’t specify “tenuous” above, though.
True. It seemed obvious in the context, but if not... "tenuous".

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

by Cousin Ricky » Sat Jan 14, 2017 3:30 pm

Chris Peterson wrote:
Cousin Ricky wrote:
Chris Peterson wrote:True. Fluids and solids can share many properties that gases do not, however. [...]
Shouldn't that be liquids and solids?
I used "fluids" deliberately, since gases, liquids, and solids are all capable of existing as fluids, and it is the fluid properties that allow something to act (at least to some degree) as a rigid, semi-rigid, or otherwise cohesive body, as opposed to a tenuous gas.
You didn’t specify “tenuous” above, though.

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

by Chris Peterson » Fri Jan 13, 2017 10:56 pm

Cousin Ricky wrote:
Chris Peterson wrote:True. Fluids and solids can share many properties that gases do not, however. [...]
Shouldn't that be liquids and solids?
I used "fluids" deliberately, since gases, liquids, and solids are all capable of existing as fluids, and it is the fluid properties that allow something to act (at least to some degree) as a rigid, semi-rigid, or otherwise cohesive body, as opposed to a tenuous gas.

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

by Cousin Ricky » Fri Jan 13, 2017 10:43 pm

Chris Peterson wrote:True. Fluids and solids can share many properties that gases do not, however. [...]
Shouldn't that be liquids and solids?

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

by Chris Peterson » Wed Jan 11, 2017 4:34 pm

earthandsky wrote:
Chris Peterson wrote:
Earthandsky wrote:Is there any indication that the tube is rolling?
I don't think it's dynamically possible for a non-rigid tube to roll. The individual particles would need to be orbiting something... and there's nothing to orbit.
Water is non rigid if you pour it, but it is if you do a belly flop into it. Measurements would decide the question.
True. Fluids and solids can share many properties that gases do not, however. In fluids and solids, the particles are highly interacting. In gases they are not. So lets say it's not dynamically possible for a rarified gaseous tube to roll (outside of the special case of it being a plasma in a strong magnetic field- a case that doesn't appear to hold for planetary nebulas).

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

by earthandsky » Wed Jan 11, 2017 4:24 pm

Chris Peterson wrote:
Earthandsky wrote:Is there any indication that the tube is rolling?
I don't think it's dynamically possible for a non-rigid tube to roll. The individual particles would need to be orbiting something... and there's nothing to orbit.
Water is non rigid if you pour it, but it is if you do a belly flop into it. Measurements would decide the question.

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

by Chris Peterson » Tue Jan 10, 2017 5:31 pm

neufer wrote:
Chris Peterson wrote:
Earthandsky wrote: Is there any indication that the tube is rolling?
I don't think it's dynamically possible for a non-rigid tube to roll. The individual particles would need to be orbiting something... and there's nothing to orbit.
It's been suggested that magnetic fields are (in part) responsible for the shape.

If so...then magnetic fields might also be responsible for some sort of rotation.
I don't think so, unless we take "rotation" very broadly. A magnetic field could cause some of the particles that are moving radially outward to follow a somewhat curved path, but the uncharged particles would still move in a straight line, and the field strength would almost certainly be so low that the amount of curvature of charged particles would be small.

It makes sense that a magnetic field could shape nebulas like this. But that would mainly be the very strong magnetic field of the progenitor star at the very start of particle ejection.

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

by neufer » Tue Jan 10, 2017 4:57 pm

Chris Peterson wrote:
Earthandsky wrote:
Is there any indication that the tube is rolling?
I don't think it's dynamically possible for a non-rigid tube to roll. The individual particles would need to be orbiting something... and there's nothing to orbit.
It's been suggested that magnetic fields are (in part) responsible for the shape.

If so...then magnetic fields might also be responsible for some sort of rotation.

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

by Chris Peterson » Tue Jan 10, 2017 3:51 pm

Earthandsky wrote:Is there any indication that the tube is rolling?
I don't think it's dynamically possible for a non-rigid tube to roll. The individual particles would need to be orbiting something... and there's nothing to orbit.

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

by Earthandsky » Tue Jan 10, 2017 3:45 pm

Is there any indication that the tube is rolling?

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

by Ann » Mon Jan 09, 2017 1:15 am

neufer wrote:
https://en.wikipedia.org/wiki/Planetary_nebula#Physical_characteristics wrote:
<<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.
Soap Bubble Nebula.
T. Rector (U. Alaska Anchorage), H. Schweiker (WIYN), NOAO, AURA, NSF
Planetaries whose progenitor stars were really no more massive than the Sun are probably intrinsically (very) faint and non-famous. But perhaps the extremely faint Soap Bubble Nebula, which is somewhat famous because it was only recently discovered due to being so faint, was really produced by a truly Sunlike star?
Constellation Guide compared the Ring Nebula with the planetary nebula that will be produced by the Sun:

The Sun will have a similar fate in about 5-6 billion years, but as it is less massive than the Ring Nebula’s progenitor star, once it becomes a white dwarf it will heat more slowly and the planetary nebula that will form once the Sun has ejected its outer layers will be much fainter because by the time the central white dwarf is hot enough to illuminate the nebula, the ejected material will be further away.
I still believe that most (at least relatively bright and obvious) planetaries in the sky have been produced by stars that were originally (considerably, or much) more massive than the Sun.

Ann

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

by Chris Peterson » Mon Jan 09, 2017 12:33 am

Ann wrote:
Chris Peterson wrote:
Ann wrote: 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.

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

by Ann » Mon Jan 09, 2017 12:17 am

Chris Peterson wrote:
Ann wrote:
Chris Peterson wrote: 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

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

by alcor » Sun Jan 08, 2017 9:45 pm

As very few planetary nebulae has a square-ish :D 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. :roll:

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

by neufer » Sun Jan 08, 2017 8:34 pm

Chris Peterson wrote:
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.

https://en.wikipedia.org/wiki/Planetary_nebula#Physical_characteristics wrote:
<<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.>>

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

by alter-ego » Sun Jan 08, 2017 7:33 pm

Chris Peterson wrote:
Cousin Ricky wrote: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).
M57 3D.JPG

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

by Chris Peterson » Sun Jan 08, 2017 5:52 pm

Cousin Ricky wrote: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?

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

by starsurfer » Sun Jan 08, 2017 5:49 pm

With yesterday's clue, I was expecting the Red Square Nebula! :D :lol2:

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

by Cousin Ricky » Sun Jan 08, 2017 5:22 pm

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?

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

by geckzilla » Sun Jan 08, 2017 5:12 pm

JohnD wrote: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.

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

by Chris Peterson » Sun Jan 08, 2017 4:31 pm

Ann wrote:
Chris Peterson wrote: 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.

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

by Ann » Sun Jan 08, 2017 4:24 pm

Chris Peterson wrote: 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

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

by Chris Peterson » Sun Jan 08, 2017 4:13 pm

neufer wrote:
Chris Peterson wrote:
NCTom wrote: 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.)

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

by neufer » Sun Jan 08, 2017 4:07 pm

Chris Peterson wrote:
NCTom wrote:
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.
https://en.wikipedia.org/wiki/Planetary_nebula#Physical_characteristics wrote:
<<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.>>
https://en.wikipedia.org/wiki/Cat%27s_Eye_Nebula#Kinematics_and_morphology wrote: <<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.>>

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

by Chris Peterson » Sun Jan 08, 2017 3:26 pm

NCTom wrote: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.

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