Eye-Like Helix Nebula Turns Blue in New Image

by Nancy Atkinson on October 4, 2012

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A combined image of the Helix Nebula from the Spitzer Space Telescope,the Galaxy Evolution Explorer (GALEX) and the Wide-field Infrared Survey Explorer (WISE).. Credit: NASA/Caltech

The Helix Nebula has been called the “Eye of God,” or the “Eye of Sauron,” and there’s no denying this object appears to be a cosmic eye looking down on us all. And this new image – a combined view from Spitzer and GALEX — gives a blue tint to the eye that we’ve seen previously in gold, green and turquoise hues from other telescopes. But really, this eye is just a dying star. And it is not going down without a fight. The Helix Nebula continues to glow from the intense ultraviolet radiation being pumped out by the hot stellar core from the white dwarf star, which, by the way, is just a tiny white pinprick right at the center of the nebula.

The Helix nebula, or NGC 7293, lies 650 light-years away in the constellation of Aquarius. Planetary nebulae are the remains of Sun-like stars, and so one day – in about five billion years – our own Sun may look something like this — from a distance. Earth will be toast.

The team from the Spitzer Space Telescope and the Galaxy Evolution Explorer (GALEX) that cooperated to create this image describe what is going on:

When the hydrogen fuel for the fusion reaction runs out, the star turns to helium for a fuel source, burning it into an even heavier mix of carbon, nitrogen and oxygen. Eventually, the helium will also be exhausted, and the star dies, puffing off its outer gaseous layers and leaving behind the tiny, hot, dense core, called a white dwarf. The white dwarf is about the size of Earth, but has a mass very close to that of the original star; in fact, a teaspoon of a white dwarf would weigh as much as a few elephants!

The intense ultraviolet radiation from the white dwarf heats up the expelled layers of gas, which shine brightly in the infrared. GALEX has picked out the ultraviolet light pouring out of this system, shown throughout the nebula in blue, while Spitzer has snagged the detailed infrared signature of the dust and gas in red, yellow and green. Where red Spitzer and blue GALEX data combine in the middle, the nebula appears pink. A portion of the extended field beyond the nebula, which was not observed by Spitzer, is from NASA’s all-sky Wide-field Infrared Survey Explorer (WISE).

Source: JPL

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

zetetic elench October 4, 2012 at 5:57 PM
newSteveZodiac October 5, 2012 at 7:01 AM

Great link, thanks!

Grimbold October 5, 2012 at 12:46 AM

[IVAN]There’s a typo in the picture caption. It should say “nebula”, not “nebual”[/IVAN]

SJStar October 5, 2012 at 5:53 AM

Wow! Doesn’t anyone in this story actually know what the central cause and evolutionary changes making planetary nebulae are?

The quoted first paragraph of the GALEX quote and UT article by Nancy is plainly incorrect (probably dumbed down too much for general consumption!)
1) Planetary nebulae have as its central star a so-called planetary nebula nucleus or PNN, and is not actually a white dwarf star — just yet. So what is the composition of this star? This is where the difference lies.

A PNN is different from a white dwarf as it still has a hot atmosphere surrounding the spent stellar core. The explanation of the important point to why this is so are;

- The energy given off makes the bright nebulosity is +100,000K PNN, but white dwarfs don’t have that power.
- On the H-R Diagram, white dwarfs occupy the line on the left-hand side of the diagram, following a descending luminosity. PNN move across the top from right to left of the diagram, maintaining a near constant luminosity for 50,000 years but changing their temperatures from 3,000K at the end of the AGB phase to the maximum of c.200,000K.
- Spectral types of PNN are like WN or WC Wolf-Rayets or O-type stars, and these are more prominent in bipolar planetary nebulae.
- There is a thick, dense atmosphere of hydrogen and other elements remain surrounding the star like an atmosphere, whose composition can be examined by spectroscopy. White dwarf have a thinner atmosphere, which is believed to be produced by diffusion.
- Theoretically, PNN are structurally different from white dwarfs, as first shown conclusively by Icko Iben Jr. in 1984.
- In most PNN models, they still have active nuclear burning shells. White dwarfs have ceased all such burning shells (unless acted upon by a companion star feeding material to the white dwarf atmosphere. When these ignite it produces the novae.

Wikipedia rightly says in the Helix. “The remnant central stellar core, known as a planetary nebula nucleus or PNN, is destined to become a white dwarf star.

2) Also you say “Planetary nebulae are the remains of Sun-like stars.

No. Not quite. Planetary nebulae formed from stars between 0.8 and 8.0 Solar Masses. A 5 to 8 solar mass progenitor are not quite “sun-like” — as these behave evolutionary quite differently. I.e. They have helium core burning. The sun will not do this because it has insufficient mass. [What you should have said is (more factually) that "Planetary nebulae are the remains of main sequence stars."]

3) Colours here are artificial made they are not real but a representation of the invisible parts of the spectrum.

4) “But really, this eye is just a dying star.” I know what you mean but this is wrong, especially as it gives the wrong impression. The PNN is the dying star, the visible nebulosity is the consequence of the superwind blown away from the star during the AGB phase. It is really evidence of a dying star. The presumed ‘eye’ is just nebulosity not a star at all.

5) “Earth will be toast.” Good. Perfectly Correct. The Earth will still probably exist, as it will be unlikely swallowed by the subsequent red giant five-odd billion years from now.

6) Older distances often quoted are closer to 700 light years (213 pc.) than 650 light years, making the dimensions of the Helix about one parsec across. Some think the distance are much closer at 159 parsecs or 520 light-years. I.e. The best being those of Stanghellini et al. “The Magellanic cloud calibration of the Galactic planetary nebula scale. (2008)

SJStar October 5, 2012 at 6:49 AM

“When a star ends its life and sheds its planetary nebula, a white dwarf is left behind.”

newSteveZodiac October 5, 2012 at 6:58 AM

Well done, the lives of stars are complex and varied both at birth and in death. APOD have this picture and a link on Central Star to a good explanation. What interests me about PNNs are the amazing patterns they form which I haven’t seen any explanations for, possibly they reflect the original rotation of the star as it sheds material out but some look like they have a magnetic field component.

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