[Spitzer-news] NASA's Spitzer Uncovers Hints of Mega Solar Systems

spitzer-news at lists.ipac.caltech.edu spitzer-news at lists.ipac.caltech.edu
Wed Feb 8 17:38:37 PST 2006


NASA's Spitzer Space Telescope has identified two huge "hypergiant"
stars circled by monstrous disks of what might be planet-forming dust.
The findings surprised astronomers because stars as big as these were
thought to be inhospitable to planets.

"These extremely massive stars are tremendously hot and bright and have
very strong winds, making the job of building planets difficult," said
Joel Kastner of the Rochester Institute of Technology in New York. "Our
data suggest that the planet-forming process may be hardier than
previously believed, occurring around even the most massive stars that
nature produces." 

Kastner is first author of a paper describing the research in the Feb.
10 issue of Astrophysical Journal Letters.
Dusty disks around stars are thought to be signposts for present or
future planetary systems. Our own sun is orbited by a thin disk of
planetary debris, called the Kuiper Belt, which includes dust, comets
and larger bodies similar to Pluto. 

Last year, astronomers using Spitzer reported finding a dust disk around
a miniature star, or brown dwarf, with only eight one-thousandths the
mass of the sun
(http://www.spitzer.caltech.edu/Media/happenings/20051129/). Disks have
also been spotted before around stars five times more massive than the

The new Spitzer results expand the range of stars that sport disks to
include the "extra large." The infrared telescope detected enormous
amounts of dust around two positively plump stars, R 66 and R 126,
located in the Milky Way's nearest neighbor galaxy, the Large Magellanic
Cloud. Called hypergiants, these blazing hot stars are aging descendents
of the most massive class of stars, referred to as "O" stars. They are
30 and 70 times the mass of the sun, respectively.  If a hypergiant were
located at the sun's position in our solar system, all the inner
planets, including Earth, would fit comfortably within its

Astronomers estimate that the stars' disks are also bloated, spreading
all the way out to an orbit about 60 times more distant than Pluto's
around the sun. The disks are probably loaded with about ten times as
much mass as is contained in the Kuiper Belt. Kastner and his colleagues
say these dusty structures might represent the first or last steps of
the planet-forming process. If the latter, then the disks can be thought
of as enlarged versions of our Kuiper Belt.

"These disks may be well-populated with comets and other larger bodies
called planetesimals," said Kastner. "They might be thought of as Kuiper
Belts on steroids." 

Spitzer detected the disks during a survey of 60 bright stars thought to
be wrapped in spherical cocoons of dust. According to Kastner, R 66 and
R 126 "stuck out like sore thumbs" because their light signatures, or
spectra, indicated the presence of flattened disks. He and his team
believe these disks whirl around the hypergiant stars, but they say it
is possible the giant disks orbit unseen, slightly smaller companion

A close inspection of the dust making up the disks revealed the presence
of sand-like planetary building blocks called silicates. In addition,
the disk around R 66 showed signs of dust clumping in the form of
silicate crystals and larger dust grains. Such clumping can be a
significant step in the construction of planets.

Stars as massive as R 66 and R 126 don't live very long. They burn
through all of their nuclear fuel in only a few million years, and go
out with a bang, in fiery explosions called supernovae. Their short
lifespans don't leave much time for planets, or life, to evolve. Any
planets that might crop up would probably be destroyed when the stars
blast apart. 

"We do not know if planets like those in our solar system are able to
form in the highly energetic, dynamic environment of these massive
stars, but if they could, their existence would be a short and exciting
one," said Charles Beichman, an astronomer at NASA's Jet Propulsion
Laboratory and the California Institute of Technology, both in Pasadena. 

Other authors of this work include Catherine L. Buchanan of the
Rochester Institute of Technology, and B. Sargent and W. J. Forrest of
the University of Rochester, N.Y. 

The Jet Propulsion Laboratory manages the Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science
operations are conducted at the Spitzer Science Center at Caltech. JPL
is a division of Caltech. Spitzer's infrared spectrograph, which made
the new observations, was built by Cornell University, Ithaca, N.Y. Its
development was led by Jim Houck of Cornell.

An artist concept of a hypergiant and its disk, plus additional graphics
and information, are available at http://www.spitzer.caltech.edu/spitzer
.  For more information about NASA and agency programs on the Web, visit
http://www.nasa.gov/home/ .

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