|
|
Annotated Image | Data Graph |
This illustration compares the size of a gargantuan star and its
surrounding dusty disk (top) to that of our solar system. Monstrous disks
like this one were discovered around two "hypergiant" stars by NASA's
Spitzer Space Telescope. Astronomers believe these disks might contain
the early "seeds" of planets, or possibly leftover debris from planets
that already formed.
The hypergiant stars, called R 66 and R 126, are located about 170,000
light-years away in our Milky Way's nearest neighbor galaxy, the Large
Magellanic Cloud. The stars are about 100 times wider than the sun, or
big enough to encompass an orbit equivalent to Earth's. The plump stars
are heavy, at 30 and 70 times the mass of the sun, respectively. They are
the most massive stars known to sport disks.
The disks themselves are also bloated, with masses equal to several
Jupiters. The disks begin at a distance approximately 120 times greater
than that between Earth and the sun, or 120 astronomical units, and
terminate at a distance of about 2,500 astronomical units.
Hypergiant stars are the puffed-up, aging descendants of the most massive
class of stars, called "O" stars. The stars are so massive that their
cores ultimately collapse under their own weight, triggering incredible
explosions called supernovae. If any planets circled near the stars during
one of these blasts, they would most likely be destroyed.
The orbital distances in this picture are plotted on a logarithmic scale.
This means that a given distance shown here represents proportionally
larger actual distances as you move to the right. The sun and planets in
our solar system have been scaled up in size for better viewing.
Little Dust Grains in Giant Stellar Disks
The graph above of data from NASA's Spitzer Space Telescope shows the
composition of a monstrous disk of what may be planet-forming dust
circling the colossal "hypergiant" star called R 66. The disk contains
complex organic molecules called polycyclic aromatic hydrocarbons as well
as silicate dust grains. Polycyclic aromatic hydrocarbons can be found on
Earth, in dirty barbeques and automobile exhaust pipes, among other
places. They are thought to be necessary for primitive life to evolve.
Silicates are essentially sand, and, in this case, were found in both
their crystalline and non-crystalline, or amorphous, forms.
The data were taken by Spitzer's infrared spectrometer, an instrument that
spreads light apart into its basic parts like a prism turning sunlight
into a rainbow. In this graph, or spectrum, light from the dust
surrounding hypergiant R 66 is plotted according to its component
wavelengths (white line). Astronomers determined the contents of this
dust by creating a model (gray line) that best fits the observations. The
model is the sum total of contributions from various types of dust grains
(colored lines).
In addition to R 66, Spitzer made similar observations of a huge disk
around the hypergiant star R 126, only this star's disk did not possess
crystalline silicate grains. Both disks might represent either an early
or late evolutionary phase of the planet-building process. In either
scenario, the possible solar systems would be supersized, with host stars
that are 30 and 70 times the mass of our sun, respectively.