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Dust in 'God's eye'

NASA / JPL-Caltech / Univ. of Arizona
A dusty disk glows red at the center of the Helix Nebula in this color-coded view.

The Helix Nebula is a popular pin-up for astronomy fans, thanks to clouds of gas and debris that make the planetary nebula look like the eye of God - or, for fans of "The Lord of the Rings," the eye of Sauron. The Hubble Space Telescope and the Spitzer Space Telescope have both taken turns producing glorious views of the Helix. Today, the Spitzer team released an even more dazzling infrared view - and as a result, there's a new dust-up over the old eye.

The reds and greens of the Helix's monstrous eye are color-coded to highlight a mystery: The infrared readings, made in 2004, have picked up the glow from a dusty disk surrounding the moribund white dwarf at the nebula's center. That's surprising to scientists, because they thought the dust surrounding the star should have been blown off in the stellar blast that created the nebula in the first place.

"The dust must be coming from comets that survived the death of their sun," the University of Arizona's Kate Su, the lead author of a research paper in the March 1 issue of Astrophysical Journal Letters, said in today's news release from the Spitzer team.

The Helix Nebula, which is about 700 light-years away from us in the constellation Aquarius, formed when a sunlike star blew off most of its outer layers. Most of the expelled gas and debris can be seen in the Spitzer image as a halo of blue-green streaks. The final layers of gas show up as the red "pupil" of the eye. The red ring at the center represents the dusty disk surrounding the nebula's parent star - something that astronomers hadn't picked up in previous images.

Su and her colleagues suggest that the dust now surrounding the star was churned up by comets smashing into each other in the chaotic aftermath of the stellar explosion. A similar phenomenon may well occur when our own sun blows up, billions of years from now.

The presence of all that material around the star may well explain yet another mystery surrounding the Helix Nebula. Past research has shown that the white dwarf was emitting surprisingly energetic X-rays - and scientists wondered where the oomph behind those X-rays was coming from.

You-Hua Chu, an astronomer at the University of Illinois at Urbana-Champaign and a member of Su's research team, said that material from the dusty disk might be falling onto the star and triggering the X-ray outbursts. "The high-energy X-rays were an unsolved mystery," Chu said in today's news release. "Now, we might have found an answer in the infrared."

For more about the mysterious Helix, read this archived Log item about the nebula's 3-D structure (including a very cool "Hubble Minute" video), as well as this one about a classic view of the eye. For more about planetary nebulae, click through this "Greatest Hits" slideshow. And if you're looking for more "Eye of God" candidates, check out the Hourglass Nebula and Fomalhaut's dusty disk.