Hints of Mega Solar Systems Uncovered
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.
illustration compares the size of a gargantuan star and
its surrounding dusty disk (top) to that of our solar
system. Click for Full Image.
"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,
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.
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.
Disks have also been spotted before around stars five times more
massive than the sun.
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 circumference.
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."
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 stars.
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 life spans 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.