A Ghostly Cosmic Pinwheel

After looking at 20 years' worth of fabulous pictures from the Hubble Space Telescope, you might get the feeling that each new release is a variation on a theme you've seen before: a supernova remnant, interacting galaxies, new stars cocooned in their placental nebulas, and so on.

Mystery pinwheel in Pegasus
A Hubble Space Telescope image reveals the delicate and intriguing spiral shape of IRAS 23166+1655. The bright but unrelated foreground star at right is 12th magnitude. Click here for a larger version.
ESA / NASA / R. Sahai
But this is something different!

The dim spiral in this image is almost spooky in its perfect symmetry. The view was captured several years ago by HST's Advanced Camera for Surveys, but a few days ago it came to light (ouch! pun alert!) on a European website devoted to Hubble's discoveries.

"So what is it?" you ask.

First, I can tell you that it's real (not an artifact), it's about 3,000 light-years away in Pegasus, and it's not associated with the bright foreground star to its right.

Second, the feature itself is designated IRAS 23166+1655, which signifies that it was spotted by the Infrared Astronomical Satellite in 1983.

"So what is it?"

It's not a spiral galaxy but rather what astronomers call a pre-planetary nebula, created when an aging, swollen star starts to shed its outer layers into space — the beginning of its death throes. In this case the shedder is an extreme carbon star, one fortified with so much carbon that there's a sooty deposit in its photosphere thick enough to block the visible light trying escape from underneath. Astronomers only know a star is there because it's still hot and thus glowing brightly in the infrared.

Archimedean spiral
An Archimedean spiral.
J?ºrgen K??ller
"But why the spiral shape?"

This isn't just any old spiral; it's a perfect fit to an Archimedean spiral, something like a jet of water coming from a spinning lawn sprinkler.

The source of this pinwheel turns out to be part of a binary system, as revealed by near-infrared images taken with the Keck II telescope. As it spews matter into space, the dying star is also slowly twirling around an unseen companion.

AGFL 3608 from Keck Observatory
Hidden from view at visible wavelengths, the double star LL Pegasi (AFGL 3608) reveals itself by heat. Its two components are 1.1 arcseconds apart. The Keck II telescope recorded this view at the near-infrared wavelength of 2.2 microns.
Mark Morris & others
Observers estimate that the ejected jet is moving outward at roughly 30,000 miles (50,000 km) per hour. Knowing that, and the angular spacing between successive rings (about 4½ arcseconds), observers conclude that they're spaced about 800 years apart. That is, if you took up a stationary position near the star, one of the outward-moving spiral's arms would sweep past you every 800 years.

As it turns out, the orbital period of the binary is also about 800 years. Consistent results!

Interestingly, the pinwheel is glowing faintly, but not from the stars hidden inside it. When Mark Morris (University of California, Los Angeles) and others took stock of this remarkable image in 2006, they concluded that the illumination source isn't the 12th-magnitude foreground star at the right — more likely we're seeing this ghostly pinwheel thanks to the combined glow of stars in the galactic plane.

If you want to explore the science behind this cosmic curiosity, here is the analysis by Morris's team, and here is a link to some work by Nicolas Mauron (CNRS, France) and Patrick Huggins (New York University).

Or you can skip the science and just be a little patient. "We have a much deeper HST observation with the new Wide Field Camera 3 now scheduled for this object in early October," Morris mentioned in an email, "so we're very excited about that."

13 thoughts on “A Ghostly Cosmic Pinwheel

  1. KPW

    That is seriously cool, and I don’t just mean that it’s only visible in the infrared. (Though that’s definitely part of it.) The more we know, the more we realize how much we still don’t know. Which means we (or someone) will still be doing this 100 years from now. I think that’s significant.

  2. Tony Flanders

    There’s no fear of running out of things to learn in the next century. In fact, astronomy is a bunch of islands of understanding in an ocean of ignorance. Most of the universe is dark energy, and it’s fair to say that we have barely a clue what that is. Most of what’s left is dark matter. We do at least have some pretty plausible theories about what dark matter might be, but we certainly know next to nothing about its properties. Everything that we can see directly — stars, the visible form of galaxies — is probably just a side-effect of dark matter.

  3. Pete

    Does any remember awhile back? I think it was in northern Norway. Somebody captured 2 nights in a row pinwheel pictures in the night sky. And some where saying that it was some kind of Russian rocket test. So, if anybody please remembers….please tell!

  4. Bill Simpson

    What is that dark lane in the galaxy in the lower right corner of the image. Is it in the galaxy, or something in the foreground blocking the light from part of the galaxy? You need to blow it up to see it.

  5. KPW

    Do a search on ‘russia norway pinwheel’ and you’ll find all sorts of stuff.

    No connection to this pinwheel though, except that they’re both Archimedean spirals.

  6. Mike T

    I’ll have to read to links to learn more of this most unusual pinwheel. I’ll have to visit the observatory at the U of A and see what other fantastic objects I can there, that I can’t see with my telescope.

  7. d m urquidi


    I have been writing a book for that past two years and have gotten all that information without Sky & Telescope and without the Hubble Telescope. I am amazed that it is almost word for word in this article.
    I never had a clue as to what I was going for, but it seems I found a good confirmation about it.

    Can I ad it to my book references?

  8. Alison

    This is very cool! Pity it took so long to be made public. The possibilities for fascinating images from the cosmos never cease to amaze me.
    Do keep us posted about the October observation!

  9. Ed-MarshallEd Marshall

    I’d like to throw in my two cents worth to a few of the comments.For “Years?”: If you look at the spinning Archimedean spiral image and image being an observer at the bottom of the spinning image, it would take 800 years for the farthest tip of the spiral from the center to make one revolution. For “Dark Lane,” I enhanced the image, and it’s just a dust lane in that galaxy. The spiral really pops out when you lighten up the image!

  10. Ed-MarshallEd Marshall

    I’d like to throw in my two cents worth to a few of the comments. For “Years?”: If you look at the spinning Archimedean spiral image and imagine being an observer at the bottom of that spinning image, it would take 800 years for the farthest tip of the spiral from the center to make one revolution. For “Dark Lane”: I enhanced the image, and it’s just a dust lane in that galaxy. The spiral really pops out when you lighten up the image though!

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  11. Jeff Largent

    Is this by any chance the start or the death of a Black Hole? I am very curious as to find this out. While it is a shame that this has not been brought out to the public earlier, it is still very beautiful to see.

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