Starship Asterisk*

JohnD wrote:
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?

JohnD wrote: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?

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

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:

[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.>>

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.

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.

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?

JohnD wrote:I was almost as lazy, geckzilla.

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

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?

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?

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.>>

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.

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?