Spitzer Puts a New Spin on the Helix Nebula (Forwarded)

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For Release: EMBARGOED until 9:20 a.m. EST, Monday, January 9, 2006

Release No.: 06-03

Spitzer Puts a New Spin on the Helix Nebula

Washington, DC -- The Helix Nebula (NGC 7293) is a challenging
stargazing target for amateur astronomers. It is one of the closest
planetary nebulas -- a type of nebula formed from gas ejected by a dying
sunlike star. Yet it is so large and spread out in the sky that it
appears very dim in a telescope eyepiece. Long-exposure photographs
unveil the true beauty of this celestial wonder. A new portrait of the
Helix Nebula, created by the penetrating infrared gaze of NASA's Spitzer
Space Telescope, is being released today at the 207th meeting of the
American Astronomical Society.

Although named for its resemblance to a coiling spiral seen face on, the
Helix Nebula has a more complex three-dimensional structure. Previous
studies showed that it consists of two gaseous disks nearly
perpendicular to each other. Observers on Earth view the main disk
nearly face on, making it appear more ring-shaped.

In addition to its overall structure, the Helix proved to be
surprisingly complex even at the smallest scale visible to Spitzer.

"Most planetary nebulas look diffuse and uniform through telescopes,"
explained Joseph Hora of the Harvard-Smithsonian Center for Astrophysics
(CfA), who leads the team that took the image. "Because the Helix is so
close, we can see more details of its fine structure. Spitzer shows that
the Helix is clumpy at very small scales."

The most striking feature of the Helix, first revealed by ground-based
images, is its collection of thousands of distinct blobs that resemble
comets due to their compact heads and long, streaming tails. Each
"cometary knot" is much larger than an actual comet, spanning about
twice the size of our solar system. Each knot holds about an Earth-mass
of hydrogen and other gases that were expelled from the nebula's central
star thousands of years ago.

In the Spitzer image, the cometary knots show peculiar color-coding with
blue-green heads and reddish tails. The bluer, more energetic radiation
at the tips comes from molecular hydrogen that has been excited by
ultraviolet radiation from the nebula's central star or shocked from its
fast-moving stellar wind. The tails lie behind the main body of the
knots and are relatively shielded. As a result, they emit redder, less
energetic radiation.

The Spitzer image shows a clear trend for the nebula as a whole to
become redder at greater distances from the central star. The clumpy
appearance extends beyond the innermost part of the nebula, although the
distinct cometary features disappear. Overall, the Spitzer image
displays a constantly changing region where powerful radiation from a
hot stellar core is blasting outward and eroding surrounding material.
Eventually, the beautiful gaseous streamers of the Helix will vanish,
destroyed by the star that created them in the first place.

The Helix Nebula is located about 650 light-years away towards the
constellation Aquarius.

The Jet Propulsion Laboratory manages the Spitzer mission for NASA's
Science Mission Directorate. Science operations are conducted at the
Spitzer Science Center at the California Institute of Technology in
Pasadena.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.

Note to editors: High-resolution images to accompany this release are
online at
http://www.cfa.harvard.edu/press/pr0603image.html