[meteorite-list] Comets Clash at Heart of Helix Nebula (Spitzer)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 12 Feb 2007 14:32:33 -0800 (PST)
Message-ID: <200702122232.OAA00806_at_zagami.jpl.nasa.gov>

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF=2E 91109 TELEPHONE (818) 354-5011
http://www=.jpl.nasa.gov

Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

News Release: 2007-014 Feb. 12, 2007

Comets Clash at Heart of Helix Nebula

A bunch of rowdy comets are colliding and kicking up dust around a dead
star, according to new observations from NASA's Spitzer Space Telescope.
The dead star lies at the center of the much-photographed Helix nebula,
a shimmering cloud of gas with an eerie resemblance to a giant eye.

"We were surprised to see so much dust around this star," said Dr. Kate
Su of the University of Arizona, Tucson, lead author of a paper on the
results appearing in the March 1 issue of Astrophysical Journal Letters.
"The dust must be coming from comets that survived the death of their sun."

Spitzer's spectacular new view of the Helix nebula shows colors as seen
in infrared and is online at http://www.nasa.gov/spitzer and
www.spitzer.caltech.edu/Media .
The dusty dead star appears as a dot in the middle of the nebula, like a
red pupil in a green monster's eye.

The Helix nebula, located about 700 light-years away in the
constellation Aquarius, was formed when a star much like our sun died
and sloughed off its skin, or outer layers. Radiation from the dead
star's hot core, called a white dwarf, heats the expelled material,
causing it to fluoresce with vivid colors. This cosmic beauty, termed a
planetary nebula, won't last long. In about 10,000 years, its shiny
clouds will fade, leaving the white dwarf and its circling comets to
cool down alone in empty space.

Astronomers have long studied the white dwarf at the center of the Helix
nebula, but nobody had detected any dust close to it until now. Spitzer,
an infrared space-based observatory, was able to pick up the glow of a
dusty disk circling around the stellar corpse at a distance of about 35
to 150 astronomical units (an astronomical unit is the distance between
our sun and Earth, which is 150 million kilometers or 93 million miles).

At first, Su and her team were shocked to see the dust. They said that
when the star died, expelling its outer layers, dust in the system
should have been blown away. The team then obtained more detailed data,
which again pointed to the presence of a dusty disk.

Where is the dust coming from? According to the astronomers, it is most
likely being freshly churned up by comets smashing into each other in
the outer fringes of the white dwarf's system. A few million years ago,
before the white dwarf formed, when it was still a lively star like our
sun, its comets and possibly planets would have been in stable orbits,
harmoniously traveling around the star. But when the star died, any
inner planets would have burned up or been swallowed as the star
expanded. Outer planets, asteroids and comets would have been jostled
about and thrown into each other's paths.

Our own solar system will undergo a similar transformation in about five
billion years. Like the Helix nebula, it will sparkle with colors. Our
sun, which will have become a white dwarf, will be circled by a band of
surviving outer planets and frenzied comets.

Spitzer has seen evidence before for such comet survivors around dead
stars. In January of last year, astronomers reported using the
observatory to find a dusty disk around a white dwarf, only the disk was
much closer in, circling at a distance of only .005 to .03 astronomical
units
(http://www.spitzer.caltech.edu/Media/releases/ssc2006-04/index.shtml).

"Finding evidence for planetary activity around a white dwarf is a
surprise," said Dr. George Rieke of the University of Arizona, a
co-author of the paper. "Finding it twice with such different properties
is a shock!"

The Spitzer data might also help explain a mystery surrounding the Helix
nebula's white dwarf. Previous observations with the German X-ray
telescope R?ntgensatellit and NASA's Chandra X-ray Observatory indicated
that the white dwarf was throwing out highly energetic X-rays. While the
white dwarf is hot, about 110,000 Kelvin (nearly 200,000 degrees
Fahrenheit), it is not hot enough to explain the energetic X-rays.
Astronomers thought that perhaps the white dwarf was accreting matter
onto itself from a hidden companion star.

But the Spitzer observations point to a different answer. According to
Su's team member Dr. You-Hua Chu of the University of Illinois at
Urbana-Champaign, material in the newfound disk surrounding the white
dwarf might be falling onto the star and triggering the X-ray outbursts.
"The high-energy X-rays were an unsolved mystery, said Chu. "Now, we
might have found an answer in the infrared."

Other authors of this work include Drs. Patrick J. Huggins of New York
University, New York; Robert Gruendl of University of Illinois at
Urbana-Champaign; Ralf Napiwotzki of University of Hertfordshire, United
Kingdom; Thomas Rauch of University Tubingen, Germany; William B. Latter
of NASA's Herschel Science Center, Pasadena, Calif.; and Kevin Volk of
Gemini Observatory, Hilo, Hawaii.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer
Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology, also in Pasadena.
Caltech manages JPL for NASA.

For more information and graphics, visit http://www.nasa.gov/spitzer and
www.spitzer.caltech.edu/Media .
Received on Mon 12 Feb 2007 05:32:33 PM PST