The Helix’s dusty heart

By Phil Plait | February 12, 2007 5:42 pm

Cool image alert!

Warning: that links to a 7 Mb image, but it’s very pretty.

What you’re looking at is one of my favorite kinds of cosmic critters: a planetary nebula, specifically, the Helix Nebula. When a star like the Sun starts to die, it bloats up into a red giant. The solar wind, a stream of particles emitted from the Sun, becomes much denser. The majority — maybe even all — of the outer layers of the star get blown off, exposing the hot white core of the star. This white dwarf is extremely dense and extremely hot, and as the last bits of the red giant are ejected, the heat from the dwarf drive the wind ever faster. The fast wind catches up with the slow wind, slamming into it, compressing it.

All manners of fantastic shapes can result. In the case of the Helix, it’s likely to actually be a flattened disk which we are seeing almost exactly face-on.

What’s interesting about this new image from the Spitzer Space telescope is the red glow in the very center. The astronomers taking this image were surprised by it.

Why? Because it indicates the presence of a disk of dust near the star. Actually, some dust is to be expected. Red giants make a lot of it, but that dust will be spread out over a huge region and may be difficult to detect. This dust is very near the core of the nebula, surrounding the white dwarf itself. Where did it come from?

The scientists think it might come from any comets that were in the system before the star died. The distance of the dust from the white dwarf is about 35 and 150 times the Earth’s distance from the Sun — the same region dominated by giant comet-like iceballs in our solar system. In the Helix, they may have survived the red giant phase of their star, and now are supplying the disk with dust during collisions. I wonder if many of the iceballs evaporated during the red giant phase as well; this would also release dust. The press release doesn’t say; I’ll have to find a paper about this.

Interestingly, this may answer another question about the Helix. It’s been known that the white dwarf gives off X-rays, more than expected for that type of star. The presence of the dust may solve that riddle. Dust streaming down into the inner regions of that now-dead solar system may interact with the white dwarf’s magnetic field, generating X-rays. That would make this discovery a twofer. Always a bonus in astronomy!

Planetary nebula are so-named because through a small telescope they appear disk-like and can be a pale green (due to the glow of ionized oxygen). For years we’ve had to explain to curious non-astronomers that they have nothing to do with planets. Now we think that as the red giant swallows up any existing planets, the shape of the nebula may be modified, so planets are involved. And now it looks like comets are as well! Funny: the Helix looks about as exotic and weird as it could, yet it also has all the signs of once being a homey place much like our own solar system. Take a good look: in a couple of billions years, we may appear very much like that nebula. And look fast, because as the wind dissipates, ever expanding, the nebula will fade. In a mere 10,000 years there won’t be anything left to see.

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures, Science

Comments (17)

  1. Aerik

    Quick! Somebody photoshop this into the eye of sauron.

  2. That Neil Guy

    So about that red color…how much of the color in this photo is “real” and how much is added? I think I recall hearing that all those marvelous Hubble (and other) images that we see are all, essentially, colorized. So would that red actually look red if we were viewing it naked eye? How does all that work? Are the colors added to indicate different parts of the electromagnetic spectrum? Or am I remebering wrong and all these colors are just out there, and if we were zooming around looking out our porthole window of our spaceship we’d see them?

  3. Spitzer is strictly infrared. So the colors are very false.

  4. TAW

    How do they determine what colors they will fake? why red and blue-green and not orange and bright purple?

  5. I printed that on my Epson R2400. Looks awesome. My office needed some colour!

  6. Chip

    What is interesting is that there are colors the human eye could detect for celestial objects under good seeing through a telescope – (not looking like the colors in the image of the Helix Nebula.) Our eyes don’t function like a camera (digital or film), but there are colors we can see. There have been a few pictures recreated to give an impression of what the eye would see under perfect conditions or if closer to the nebula. It is not necessarily brighter, just more detailed.

    Most pictures I’ve seen in books and onm line are false colors designed to enhance specific gases or chemistry.

  7. RPink

    If I keep downloading these large satellite photos, I’m going to run out of hard drive space. :P

    I still have that 7872×8952 Tarantula Nebula image on here from your “Best of 2006″ post. It has some stunning detail. Amazing.

  8. wright

    I had no idea planetary nebulae were so ephemeral… 10,000 years is it? Wow.

  9. Troy

    The storm on Neptune when Voyager visited (1986) was called the “Wizard’s eye”, ground based observations showed that it disipated a few years later. Now that seems much more a wizard’s eye than the Neptunian storm every was!

  10. Good grief-
    I’m so tired commenting on the BA’s post concerning Christianity and evolution I don’t have any time left today to read this science article.

    What does that say about me?

  11. Melusine

    I think I recall hearing that all those marvelous Hubble (and other) images that we see are all, essentially, colorized. So would that red actually look red if we were viewing it naked eye? How does all that work? Are the colors added to indicate different parts of the electromagnetic spectrum?

    That Neil Guy, The Hubble Site has a useful slideshow of how and why Hubble’s photos are colorized (you can play with a few pictures, too). For some reason it’s not formatting right on my PC, but you can click and highlight the words down to the “next” button on the lower right:
    http://hubblesite.org/gallery/behind_the_pictures/

    It’s an interesting and important question, and one that’s come up here before. What color would Mars’ surface look like if we were actually standing there? And so on…

    Stunning picture!

  12. Grand Lunar

    I saw this on NASA’s webpage not long before I found it here. Ah, connections in cyberspace…

    Moving along, it’s facinating that we can find signs of comets in such a distant location. Yet another fantastic feat for the modern era of astronomy!

  13. We finally found the Eye of God! The Moties can’t be far behind!

  14. Sorry if my link in the last post didn’t work – it was to this Wikipedia entry for the Larry Niven/Jerry Pournelle novel, The Mote in God’s Eye – http://en.wikipedia.org/wiki/The_Mote_in_God's_Eye

  15. Peter Bramley

    If you were at the nebula would you be able to see it? Or are the particles too dispersed to see up close and only visible because we are so far away?

  16. That Neil Guy

    “The Hubble Site has a useful slideshow of how and why Hubble’s photos are colorized (you can play with a few pictures, too). ”

    Thanks, Melusine, for that link to the hubble site. Great info, very helpful — and interesting!

  17. Irishman

    Anyone else notice the purple “heart-shape” in the second image? Happy Valentine’s Day!

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