Starship Asterisk*

A Spiral Nebula Surrounding Star R Sculptoris

Explanation: What's happening around that star? An unusual spiral structure has been discovered around the Milky Way star R Sculptoris, a red giant star located about 1,500 light years away toward the constellation of the Sculptor (Sculptoris). The star was observed with the new Atacama Large Millimeter/submillimeter Array (ALMA), the most powerful telescopic array observing near millimeter wavelengths, that part of the spectrum situated well beyond red light and between microwaves and radio waves. Data from ALMA observations was used to create a 3D visualization of the gas and dust immediately surrounding the star. A digital slice through this data showed the unexpected spiral structure. Although unusual, a similar spiral pattern was discovered in visible light recently around LL Pegasi. Upon analyzing the data, a hypothesis was drawn that the red giant star in R Sculptoris might be puffing gas toward an unseen binary companion star. The dynamics of this system might be particularly insightful because it may be giving clues as to how giant stars evolve toward the end of their lives -- and so release some constituent elements back to the interstellar medium so that new stars may form.

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http://asterisk.apod.com/viewtopic.php?f=31&t=29737

The date shows October 15. It should be October 16

abhagwat wrote:The date shows October 15. It should be October 16

Thanks, I emailed them.

Well...the star is spinning....why wouldn't it be a spiral?

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Hi,

An astronomer who comes up with a powerful hypothesis may be called 'insightful', but a star cannot be, lacking consciousness. What is apparently meant is something like "provides an opportunity to gain insights about stellar mechanics"

The star in this APOD is an interesting but mild kind of "spiral star". If you want a big one, check out this spinning Wolf-Rayet massive star!

Ann

jingming wrote:Hi,

An astronomer who comes up with a powerful hypothesis may be called 'insightful', but a star cannot be, lacking consciousness. What is apparently meant is something like "provides an opportunity to gain insights about stellar mechanics"

• Perhaps "instructive" was the intended word.

Fortunately, the APOD editors are indeed astronomers and not English majors. This means you can't really get into a good argument with them about such things. They try their best.

I'm wondering about the orbiting time of the companion, or the rotation speed of the star itself.
If this feature is at 1500 light years away, it must be of considerable size. So the orbiting or rotation must be very, very slow in order to produce a spiral like this. So, if it is a companion, it can't be close to the star, and if it isn't close, how can it produce such an effect?

Beluga wrote:
I'm wondering about the orbiting time of the companion, or the rotation speed of the star itself.
If this feature is at 1500 light years away, it must be of considerable size. So the orbiting or rotation must be very, very slow in order to produce a spiral like this. So, if it is a companion, it can't be close to the star, and if it isn't close, how can it produce such an effect?

Unlike the Beta Lyrae situation, the companion R Sculptoris star is NOT pulling off material

Rather, the magneto-tail of companion R Sculptoris star is sculpting the strong solar wind plasma of the primary star.

http://www.o.org/public/archives/releases/sciencepapers/eso1239/eso1239a.pdf wrote:
The inner windings have a nearly constant spacing of average distance of 2.6” ~ 189 billion kilometers.

The R Sculptoris solar wind speed ~ 17.1 km/s.

• Hence: the orbital period of the companion R Sculptoris star ~ 350 years.

Would the outer "rings" of the spiral be closer together the further they travel from the originating star considering that their escape velocity would eventually slow? Or would they slow down at all?

quigley wrote:
Would the outer "rings" of the spiral be closer together the further they travel from the originating star considering that their escape velocity would eventually slow? Or would they slow down at all?

The outer "rings" of the spiral are closer together the further they travel from R Sculptoris in small part due of gravitational breaking; however, magnetic field effects due to both stars (and the outer interstellar space) are really dominating the dynamics.

Do we know why the spiral shape (whether in visible or invisible light) seems to be so rare? Might a spiral be caused by emissions from just one area of a spinning star? Like water from a hose being swung around like a lasso?

Thank you for your tremendous public service. I have been an avid follower since I heard about about APOD in a lecture given by Dr. Andy Fabian of Cambridge several years ago. As exquisite as the photos is the writing! Kindest Rgds, Philip Shull

If the spiral shape is rare, what isn't rare? I think spirals are one of the most common natural forms in the universe, at least as far as I've noticed. That, and spheres.

Anyone know the angular size of this nebula? I would like to know how our solar system would fit into the picture.

Philip Shull wrote: Do we know why the spiral shape (whether in visible or invisible light) seems to be so rare? Might a spiral be caused by emissions from just one area of a spinning star? Like water from a hose being swung around like a lasso?

Given the size of the nebula and speed of the stars 'solar' wind, the rotation of the star would have to be many years - neufer quoted 350 years. I'm not an astrophysicist, but I don't think that stars rotate that slowly, and even if they did, I know of no reason why emissions would be from just one area of a spinning star for so long.

Craig Messerman wrote:Anyone know the angular size of this nebula? I would like to know how our solar system would fit into the picture.

Neufer quoted a source which said:

The inner windings have a nearly constant spacing of average distance of 2.6” ~ 189 billion kilometers.

The distance between the Sun and the Earth is about 150 million kilometers. It seems to me that if neufer's source is correct, then the average distance between each inner winding of this spiral is ~ 1,000 times the distance between the Sun and the Earth.

Ann

FLPhotoCatcher wrote:

Philip Shull wrote: Do we know why the spiral shape (whether in visible or invisible light) seems to be so rare? Might a spiral be caused by emissions from just one area of a spinning star? Like water from a hose being swung around like a lasso?

Given the size of the nebula and speed of the stars 'solar' wind, the rotation of the star would have to be many years - neufer quoted 350 years. I'm not an astrophysicist, but I don't think that stars rotate that slowly, and even if they did, I know of no reason why emissions would be from just one area of a spinning star for so long.

The "350 years" that neufer quoted doesn't refer to the rotation of the red giant star, but to the orbital period of its companion.

For example, it takes the Earth 24 hours to rotate one full turn, but its orbital period around the Sun is 365 days.

Ann

I see no evidence of a binary companion. And I see no reason how such an object can cause a spiral of such dimensions.

The outer ring is actually a dis-connected circle; the inner regions show more spiral characteristics. The configuration of the nebula is indicative of how the star is ejecting material from its surface. The first ejection was very fast, much faster than the rotational speed of the star. Hence, a very distinct equatorial circular outer ring of material was formed. Later ejections became less powerful, but still created less distinct circular rings of material. The earliest ejections are much less powerful and the ejecta velocities are much closer to the rotational speed of the star thereby creating the very distinct inner spiral that is being discussed.

That is my "take" on this very interesting red giant nebula,
Doug

dougettinger wrote:I see no evidence of a binary companion. And I see no reason how such an object can cause a spiral of such dimensions.

The outer ring is actually a dis-connected circle; the inner regions show more spiral characteristics. The configuration of the nebula is indicative of how the star is ejecting material from its surface. The first ejection was very fast, much faster than the rotational speed of the star. Hence, a very distinct equatorial circular outer ring of material was formed. Later ejections became less powerful, but still created less distinct circular rings of material. The earliest ejections are much less powerful and the ejecta velocities are much closer to the rotational speed of the star thereby creating the very distinct inner spiral that is being discussed.

That is my "take" on this very interesting red giant nebula,
Doug

Camille Carlisle on the Sky and Telescope website gives a clear explanation of how an orbiting binary star could create this spiral nebula.

http://www.skyandtelescope.com/news/Sta ... 87651.html

Anthony Barreiro wrote:
Camille Carlisle on the Sky and Telescope website gives a clear explanation of how an orbiting binary star could create this spiral nebula.

http://www.skyandtelescope.com/news/Sta ... 87651.html

Ahhh.... so it's the speed modulation of the primary is it.

dougettinger wrote:I see no evidence of a binary companion. And I see no reason how such an object can cause a spiral of such dimensions.

The outer ring is actually a dis-connected circle; the inner regions show more spiral characteristics. The configuration of the nebula is indicative of how the star is ejecting material from its surface. The first ejection was very fast, much faster than the rotational speed of the star. Hence, a very distinct equatorial circular outer ring of material was formed. Later ejections became less powerful, but still created less distinct circular rings of material. The earliest ejections are much less powerful and the ejecta velocities are much closer to the rotational speed of the star thereby creating the very distinct inner spiral that is being discussed.

That is my "take" on this very interesting red giant nebula,
Doug

The reason why you don't see the companion is likely because the companion is so very much fainter than R Sculptoris itself. Remember that R Sculptoris is likely at a late evolutionary phase where it is extremely bright for its mass. The companion, which is likely less massive than R Sculptoris, is probably unevolved and very much less bright. I have read somewhere that when the Sun becomes a red giant, it will undergo phases where it is briefly at least a thousand times brighter than it is now.

Also note that this picture was taken by a telescope which detects wavelengths that are much longer than visible light. A cool star like R Sculptoris will show up well here, but an unevolved companion whose temperature is comparable to that of, say, the present-day Sun, will likely be undetectable in an image like this unless special processing is made to bring it out.

But even if the companion is certainly very much less bright than R Sculptoris, it doesn't have to be much less massive. It could very well strongly affect and shape the outflows from R Sculptoris.

Ann