Thus spoked the Dumbbell

By Phil Plait | September 7, 2011 6:30 am

My love for planetary nebulae is on record. These expanding shells of gas from dying stars are really beautiful, and I find the physics of the way the gas is ejected to be fascinating. I’ve written about them a lot: check the Related Posts at the end of this article for links.

I like to observe them, too. In the summer there are quite a few that are easy targets, and one of the easiest to find is called M27, the Dumbbell. It’s in the constellation of Vulpecula (the fox), and is big and bright enough to spot easily in binoculars. I’ve probably seen it with my own eyes, no lie, hundreds of times.

But I’ve never seen it like this:

[Click to ennebulenate.]

Holy wow! That’s so cool! Literally: this is an infrared image taken by the Spitzer Space Telescope, showing it in light well beyond what our eyes can perceive.

That’s not at all how I’m used to seeing it! Inset here is an image in optical light (the kind our eyes see) taken by the Kitt Peak 2.1 meter telescope. You can see why it’s nicknamed the Dumbbell; it looks like it has a handle and two curved weights on the ends. The ends are really just bright regions of an outer limb-brightened shell, and the handle is gas inside the nebula.

In infrared things are so different! Most striking are those incredibly long and thin spokes, stretching away radially from the center. Things like this have been seen before; the Helix nebula, for example, has something similar. But in the Helix they’re fatter and not as long. I wondered at first if perhaps in the Dumbbell these were not actual structures, but instead optical effects like rays from the setting Sun. Maybe the gas in the nebula was blocking the central star’s light, and holes were letting these rays through…

… but nope. I was wrong. These are actual, real, physical structures! Like in the Helix (the image inset here, taken by Hubble), the nebula is littered with dense knots of material, probably condensations in the wind blown from the dying star when it was a red giant. As the outer layers of the star blew away, they exposed deeper, hotter material. The wind from the star increased in speed, overtaking and blowing past the older material the star had emitted centuries before. When the faster wind hit denser knots of gas, it flowed around it, and also vaporized the surface material of the knots. This material then got swept "downwind", blowing off the knots and forming those long, long streamers. They look a lot like comets, actually, and the physics is similar.

I was surprised the spokes could be so long, but then remembered the image at the top was in the infrared. This is cooler material, and can be traced farther out from the nebula than it could in optical light. Also, as it happens, the spokes in the Dumbbell are just physically really long (they are a couple of light years in length, in fact). I was surprised you could get coherent structures of that length in a nebula like this… but then, planetary nebulae are surprising beasts! That, and their literally other-worldly beauty, are two of the reasons I love them so.

Image credits: Spitzer: NASA/JPL-Caltech/Harvard-Smithsonian CfA; Optical image: REU program/NOAO/AURA/NSF; Hubble image: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO).

Related posts:

Hubble sees a gaseous necklace 13 trillion km across
Warm dusty rings glow around a weird binary star
Awesome death spiral of a bizarre star

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (14)

  1. david germain

    its interesting that there are no turbulence eddie’s showing in the downwind legs of the dark spots.
    The wind hits the object then appears to flow straight round with no which i would describe as back filling.
    illustrated very well in the following video..
    I would have thought that the eddies would help in star and planet formation. giving partials chance to enter orbit and then create a accretion disk.

    if you have any thoughts on this i would love to hear them.

    cheers dave

  2. When images of the Helix nebula’s spokes first came out, I wondered if those dense knots were centered around whatever planets or other solid objects had once been orbiting the star before it blew. Then I realized the scale was all off by several factors. Durnit.

  3. VinceRN

    Once again seeing these images makes me want to kick my 8″ Newt. I need a space telescope!

  4. Posts like this are exactly why I come here everyday. Incredible space imagery and thoughtful analysis to explain the beauty. Rock on.

  5. DennyMo

    When I first saw the title, I figured it would be a post about Rick Perry, then I saw the “d” at the end of the second word…

    VinceRN, next time you want to kick your 8″ Newt, give me a call. I’ll come over and exchange your 8″ for my 4″, then you can kick as much as you want. :)

    BA, thanks for posting these!

  6. Anthony D.

    @ Vince and Denny

    At least having a telescope is better than nothing. Lol.
    The dumbbell is one of my nightly visits. I usually start with the ring nebula then pan over to the dumbbell afterwards. I love PN also, just amazing beauty in something so destructive.

  7. Anthony D.

    I forgot to mention that we are all, and everything around us, a result of these beautiful sights.

  8. It’s a bow-tie. Bow-ties are cool.

  9. PaulV
  10. Jess Tauber

    SO…if there are intelligent creatures living there, would that make them ‘spokespersons’…?

  11. Messier Tidy Upper

    @ ^ Jess Tauber : LOL. 😉

    Any creatures living there would certainly have an interesting environment to contend with – although the prospects of any indigenous aliens ( 😉 ) surviving their star ballooning into a red giant then becoming a Mira variable and planetary nebula seem remote.

    I wonder if the morphology of this planetary could perhaps give us clues as to whether any exoplanets used to orbit the star that has formed Messier 27 existed (or even still exist) – and what their nature might’ve been?

    Awesome image there. :-)

  12. Anchor

    There was never much question that the radial structures in the Dumbbell wasn’t purely crepuscular (“optical effects”) in nature, or they would have been as apparent at optical wavelengths and well known to us long since.

    On the other hand, imagine the expanding outer atmosphere of the newly-turned white-dwarf Sun impinging upon the legion of icy cometary objects we KNOW FOR A FACT populate the Kuiper Belt and surrounding Oort Cloud reservoir out to a radius of up to a light-year. Consider further that it is possible for them to have had lots of time to dynamically congregate in loosely-held clusters far from the gravitational influence of any of the major inner planets, and won’t have been frequently disturbed from the rare relatively close encounters of interstellar interlopers (stars and brown dwarfs) over the course of the Sun’s very long 10-billion-year lifespan by then.

    It is hard to imagine a hot and sustained (if rarefied) stellar outflow NOT producing these very same kinds of cometary radial structures out of such a populous surrounding flock of icy objects commonly thought to attend most all sun-like stars.

    Yet I LIKE the scenario suggested by García-Segura et al in 2006 (and others who suggested it years earlier) as a mechanism for radial structure in ‘planetary nebulae’. It seems to work, but like so many other complex phenomena in nature, one chooses a SINGLE explanation to explain EVERYTHING in a complex phenomenon at one’s peril. Nature isn’t obliged to select a winner out of pathetically limiting dichotomies (excruciatingly dumb “either this or that explanation is correct”) – especially those dreamed up by unimaginative humans. One might as well expect that the deployment of an oak tree is completely dertermined at the genetic level without any input from its environment, as if the acorn had all the instructions that dictated how every branch should grow and every leaf should fall.

    While the García-Segura et al scenario may indeed be an important mechanism for radial structure in most cases, I would like to see a lot more work showing how clusters of icy objects in an outer envelope around dying stars CAN’T be responsible for any of the very same beautiful effect.

    That work has not yet been adequately addressed.

    The ultimate irony here is that if EITHER or BOTH of these two mechanisms are primarily operative – or NEITHER of them are – the phenomenon of crepuscular radiance is NECESSARILY PRESENT ANYWAY! It can’t be avoided because of the obvious variations in the density posed by the cloud clumps we see in such nebulae like the Helix (although the visible effect of a crepuscular contribution to the radial structure might be quite slight compared to that of the primary causes). So there are at least THREE ways of producing or enhancing radial structure in Stellar Terminal Nebulae.

  13. It’s a bow-tie. Bow-ties are cool

  14. Matt B.

    Was the name Apple Core Nebula already taken? Because seriously, it’s an apple core.


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