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

Comments and questions about the APOD on the main view screen.
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Ann
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Re: APOD: IC 4406: A Seemingly Square Nebula (2017 Jan 08)

Post 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.

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

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

Is there any indication that the tube is rolling?

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

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

Post 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.
Art Neuendorffer

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

Post 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.
Chris

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

Post 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.

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

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

Post 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?

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

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

Post 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.

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

Post 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".
Chris

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