A dying star weaves a spiral in the night

By Phil Plait | October 10, 2012 11:01 am

The number of ways stars can find to die bizarre deaths will never cease to amaze me.

Some explode, supernovae which blast radiation across the Universe. Others fade away slowly over hundreds of billions of years, longer than the cosmos has been around. Some blow off winds of gas and dust, taking on strange shapes from perfect spherical shells to elongated structures that look like two jellyfish kissing.

And then some – a very few – are like R Sculptoris, a red giant on the thin hairy edge of death. And its death is both spectacular as well as just plain old damned weird.

Check THIS out:

This is not a drawing! It’s actual data, observations of R Sculptoris made using the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA looks at light far too low energy for our eyes to see; it’s actually out past infrared in the spectrum. Cold dust and gas emits light at this wavelength, including carbon monoxide. That molecule is created copiously in red giants and shines brightly in the submillimeter, making it easy to see with ‘scopes like ALMA. That’s nice, because CO can be used as a tracer for other, harder to detect molecules like hydrogen. Looking at CO really tells you a lot about what’s going on in the gas and dust.

And what’s going on? Ah, this is the really cool part.

When a star like the Sun (either a bit less massive, or up to about 8 times as massive) ages, the core heats up, which causes the outer part of the star to expand (like a hot air balloon), turning it into a red giant. The details are complicated – read this post on a similar star where I explain it in more detail (and you want to because the details are awesome) – but the bottom line is that helium builds up in a thin shell outside the star’s core, where it fuses into carbon. The fusion rate is insanely sensitive to temperature, and periodic imbalances in temperature cause vast and very sudden increases in the fusion rate – and by sudden I mean over a timescale of just a handful of years, the blink of an eye to a star. Called a thermal pulse, this huge fireball of energy is dumped into the star’s interior, blows upward like a tsunami, and then blasts material clear off the star’s surface.

The result is an epic paroxysm which blows out a massive wave of material, expanding in a sphere around the star. We’ve seen this before, like in the star U Cam. After a few years, you get an eerie detached shell of expanding material, like a smoke ring trillions of kilometers across.

OK, so that’s the thin shell thing on the outside. So what’s the deal with R Sculptoris that makes that freaky inner spiral pattern?

I’m glad you asked! Unlike U Cam, R Sculptoris has a companion. It’s probably a smaller star, like a red dwarf or even something more like the Sun. It orbits the red giant once every 350 years, or, to be more accurate, the two stars orbit each other. As material from the red giant expands outward, the combined spin as the two stars’ dance forms the spiral pattern.

It’s like a rotating garden sprinkler. Each drop of water from the sprinkler goes straight outward, but each at a slightly different angle – like one drop heading due north, the next slightly east of north, the next slightly east of that, and so on around the compass points. To our eye, this looks like an expanding spiral, even though it’s made of individual drops moving radially out from the center. It’s an illusion of sorts.

This video might help. It was made using the ALMA observations, and shows the star starting about 250 years before the pulse. We see material expanding, then at t=0 there is the big pulse, forming the shell and spiral:

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[If the video doesn’t load, refresh this page, or try this link.]

Amazingly, we’ve seen this sort of thing before too. LL Peg has a spiral of material around it, formed in much this way. Interesting: U Cam has the shell with no spiral, and LL Peg has a spiral with no shell. R Sculptoris is more awesomer than them, because it has both.

R Sculptoris has both a shell and a spiral because the thermal pulse had a very sudden, sharp beginning, but continued to drive material off the star’s surface for many years after that first wave. That initial blast expanded rapidly, so rapidly compared to the orbital period of the second star that it was essentially instantaneous. In other words, there wasn’t time to imprint the spiral pattern on it; it expanded outward in a spherical wave. It eventually collided with material previously ejected by the star, got compressed it, and formed the the thin shell. But back at the star the pulse continued, blowing off more material over time. That was slow enough that the orbital motion of the two stars affected the expansion, creating the spiral pattern.

Amazing. But there’s more!

Using the ALMA observations combined with models of the star’s behavior, the scientists have found that this last pulse occurred 1800 years ago and lasted for 200 years. They were also able to estimate the amount of material blown away from the star: about 0.3% of the mass of the Sun.

Doesn’t sound like much, does it? Well, let me rephrase that for you: the mass ejected by this star in this two-century long event was a thousand times the mass of the Earth. Oh, and did I mention that all this material was blasted outward at 50,000 kilometers per hour?

The energy it took to eject this much material at this speed is very roughly the same amount of energy the Sun puts out over the same time period. So that thermal pulse added as much energy to R Sculptoris as our entire Sun emits. That’s actually rather terrifying.

But also very, very cool. Like I said way back at the beginning, it’s truly astonishing how many ways stars find to die. In that way they’re like people: some live their lives brightly and fast, blowing out in spectacular fashion, while others live dimly and just fade away. But others live normal lives, going about their everyday business, but when the day finally comes, they find the wherewithal to go out in truly amazing and heroic fashion.

Wait. Was I talking about stars or people?

Image credit: ALMA (ESO/NAOJ/NRAO); Video credit: Nature/M. Maercker et al./S. Mohamed/L. Calçada

Related Posts:

Awesome death spiral of a bizarre star (and trust me, you really want to click on that link)
The ghost in the shell
Similar by eye, not by nature
Awesomely bizarre light show freaks out Norway (and a followup)

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (30)

  1. My mind is being blown in a spiral pattern.

  2. Hi Phil, I actually created the image above at ESO, and although you are right on saying that it is indeed actual data, I’d be careful saying it is not a drawing. We took some liberty on interpreting the data from the scientists and creating the final look. I say this because it can be misleading and people might think that ALMA actually took THAT image. That image is a reconstruction, using the data as source. Sort of borderline case, and this might be interesting to stress out.

  3. gameshowhost

    That’s cool.

    /read in paris hilton’s voice, but not.

  4. Tara Li

    It doesn’t look *that* much like a spiral to me – more of a series of shells from repeated pulses. Is there some way to actually confirm the spiral structure as being real, rather than pareidolia?

  5. Jim Tim

    It didn’t look like a spiral at my initial examination, but start with the outer shell @ 3:00 and you can see the spiral start, its a bit messy between 12:00 and 9:00 but you can continue to keep tracing it inwards. It is very noticeable near the center.

  6. Luis C (#2)- Thanks for the note. Can you elaborate a bit? On the ESO page it doesn’t say how the image was created, and I assumed it was using the actual data after some cleaning (deconvolution or whatever technique is used these days in radio astronomy). I put in some weasel words in the post and linked to your comment. :) Thanks!

  7. Looks like Sauron is tripping balls!

    And a quick grammatical correction, Phil:
    Interesting: U Cam has the shell with no spiral, and LL Peg has a spiral with no shell. R Sculptoris is more awesomer than them, because it has both.

    That should be “R Sculptoris is moar awesomer than them, because it has both.” ūüėČ

    Also, is it just me or does LL Peg bear a remarkable resemblance to that Russian rocket (actually, I think there have been several at this point) that created a spiral during launch when venting fuel while spinning?

  8. Jerome

    Just what do you think you’re doing, Dave.

    Watch the video, you’ll understand.

  9. Gary Ansorge


    You always bring me the best violence,,,er,,,stars going blowey uppie…


    Gary 7

  10. CB

    The spiraling shape will make you go insane.

    … and I’m happy to be here.

  11. Atalanta

    As an Uzumaki fan, I had a brief moment of “eek”!


    It’s also reminds me of the Norway missile incident – I was wondering if I would be the only one who found it eerily similar.

  13. Messier Tidy Upper

    Wow. Superluminously stunning image and superb write-up. Thanks Phil. 8)

    One question – are we looking at a star or a protoplanetary nebula here? Guessing the latter but its still in its red giant phase so, a little puzzled over its exact classification.

    @12. NAVSTAR : I think you’ll find (#7.) Joseph G beat you to that but yeah, distinct similarity, similar cause, similar pattern massively different scale of object! ūüėČ

  14. Guilherme

    shibalba from The fountain ??? ūüėČ

  15. Messier Tidy Upper

    Just thought – if this is a red giant star is it also some kind of variable eg. Mira, semi-regular, long period?

    The designation “name” R Sculptoris certainly tends to strongly suggest that.

    If so how does that R Sculptoris’s variability the pattern and might it illuminate it or different parts of it better in some times than others?

    Could we follow R Sculptoris over a variable cycle and see what that does to alter the appearance of the surrounding nebula /(protoplanetary?) shell?

    Plus could this sort of process explain the apparent non-spherical nature of some Mira stars including the eponymous Omicron Ceti itself?

  16. Messier Tidy Upper

    See :


    Which notes :

    In a 1996 press release (no. STScI-PR96-26), NASA revealed that Hubble’s Fine Guidance Sensors (FGS) had retrieved data showing that perhaps not all Mira stars are spherical, but may be somewhat egg-shaped. … (snip -ed.) … In addition, an impressive account of size of these objects was also given: “If placed within our solar system, both of these stars would extend well beyond the orbit of the Earth and almost to Jupiter.”

    The observed asymmetry is believed to take place in the extended atmosphere of the star, but the exact cause is currently not understood. It is speculated that the odd shape may be a result of nonradial pulsations (the star not pulsating equally in all directions) or could possibly be an optical illusion as a result of large dark spots on the star, perhaps caused by giant convection cells (Lattanzi et al. 1997). The first indications of this oblong shape were detected in Mira, but through interferometric means have been observed in the stars R Cas, R Leo, and W Hya as well (Karovska 1997).

    (Emphasis added.)

    So now wondering does that extended atmosphere include the spiral shell here?

    See also :


    an ESO zoom in animation to R Sculptoris with initial photographic finder chart.

    Plus :



  17. Messier Tidy Upper

    @9. Gary Ansorge :

    Phil, You always bring me the best violence,,,er,,,stars going blowey uppie…
    Cool! Gary 7Gary

    Yeah, he sure does. But then the BA is the bringer of Death from the Skies after all! Also, hey, I thought you were a hippy non-violent type! ūüėČ

    (BTW. Good to see you commenting here again – don’t recall seeing you comment for a while here, good to have you back.)

  18. I’m thinking about that scene from Contact when Jodie Foster is awestruck at the magnificence of the cosmos and has “no words” other than to say “They should have sent a poet”.

    You’re a poet.

  19. Captain Janeway
  20. Messier Tidy Upper

    BTW. Does anyone know the spectral type, distance from our Sun and magnitude range for R Sculptoris and care to enlighten us here please?

    I’ve searched and been unable to find – it has neither a wikipedia page nor yet a listing on Kaler’s Stars website.

    Anyone here ever observed it as a variable?

  21. Tara Li

    es.wikipedia.org has an article on R Sculptoris (Spanish, English translation by Google):

    Sculptoris R (R Scl / HD 8879 / HR 423) is a variable star in the constellation of Sculptor . It is an interesting target for the amateur astronomer , combining a wide range of variability, excellent stars with which to compare and intense red.

    At a distance of about 1550 light years , R Sculptoris is a carbon star of spectral type C6II. In these stars the carbon compounds allow passing blue light, so show an intense red. Large amount of material lost its outer layers through the stellar wind , in some of them there is a separate layer of gas and dust that surrounds them. Although generally dominated by a single temperature, some Sculptoris-R-like show evidence of a secondary cooler powdery component, which is manifested by an excess infrared remote. It is thought that this excess is due to the existence of a layer of dust removed from the star.

    Sculptoris R is a semiregular variable star whose brightness varies between apparent magnitude +12.90 +9.10 and throughout a period of 370 days. The amplitude of the oscillation appears, however, variable.

    Visually a 10 arcsec there a companion star of magnitude 11.9, which shares proper motion with R Sculptoris.

  22. Messier Tidy Upper

    @ ^ Tara Li : Excellent – just what I was after! Thanks. :-)

  23. Luis C.

    @Phil (#6)
    Just to clarify and avoid misunderstanding. These are indeed actual data, as you originally stated! But it is not a image as in the good old days where only CCDs roamed the skies… ALMA data are different and here they’ve been visualised in a slightly different way from how we normally treat a plain two-dimensional CCD picture. One of ALMA’s great strengths is that its observations also have a spectral (wavelength) dimension in addition to the “x” and “y” dimensions of RA and Dec. So for every “pixel” on the sky, we actually get a spectrum from that point, i.e. the dataset is a three-dimensional data cube rather than a two-dimensional image.

    We wanted to show a three-dimensional view of the structure in the data, which you can see rotating in the top-left of the video at http://www.eso.org/public/videos/eso1239a/ . We rendered the data points using glowing particles in order to let the viewer see through the surface into this 3d structure. We also added a marker in the centre to represent the central star. The main image from our release, which you’ve shown above, is a 2d slice through this 3d rendering of the ALMA datacube. The short answer: yes, these are definitely real data and in no sense a “drawing”!

  24. Tara Li

    @5 Jim – I know that looking at it, it’s not hard to see a spiral. My question is if actual mathematical curve-fitting was done to distinguish. After all, the BA-Man has shown us example after example of how the eye and the mind work together to create patterns that aren’t necessarily there.

  25. Mattais

    Am I correct in my interpretation that you are using the doppler shift in the spectrum of each ALMA pixel to derive the 3d position of each point around the star?


  26. Dustin

    @23 Luis C. – Thank you for adding the additional information. Seeing the 3d interpolation of the data is probably one of the most amazing things I have seen in a while. To actually give these astronomical objects real shape makes these wonders come alive. It sparks the imagination! Thank you and thank you Phil for sharing the wonders of our Universe with all of us,

  27. Jon Hanford

    @Joseph G(7)

    The HST image of LL Peg always reminds me of the (completely unrelated) dwarf “elliptical” galaxy IC 3328 in the Virgo galaxy cluster:



  28. Lawrence

    The explanation for all this is simple. We are watching an alien civilization constructing a Dyson sphere.

  29. Matt B.

    So we have only two examples of the spiral so far, right? And they both seem to be oriented pretty normal to us. So I’m guessing that a spiral would be difficult to discern if it’s far from normal. Otherwise it’s a big coincidence.


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