Unlocking the Keyhole - and finding
Kangaroos!
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Media Release - School
of Physics - The University of New South Wales
Tuesday 11th January 2000
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Using telescopes at the South Pole
and in Australia, astronomers at the University of New South Wales
have unlocked the Keyhole nebula, a cloud
of gas associated with massive star formation. The true nature of
the region was discovered through the use of infra-red images revealing
that the clouds of gas in the region are being heated and are `glowing'
as a result of the radiation coming from the massive stars in the
area.
The images taken at the South Pole are
amongst the first ever obtained with a new infra-red telescope (called
SPIREX). This telescope exploits the extremly cold, dry and stable
conditions at the South Pole to take more sensitive images in the
infra-red than can be obtained anywhere else on the Earth. SPIREX
has been developed by the UNSW astronomers in conjunction with colleagues
in the USA. The images taken with SPIREX reveal extensive emission
from organic molecules (such as polycyclic aromatic hydrocarbons
or PAHs) that pervade the cloud.
The Anglo Australian Telescope equipped
with a special infra-red camera (called UNSWIRF)
was also used to obtain infra-red images of the Keyhole nebula.
This instrument was also developed by the UNSW astronomers and allows
them to take pictures of the emission from hydrogen molecules. This
emission was found to be almost identical (in intensity and morphology)
to the emission from the organic PAH molecules.
The region around the Keyhole nebula
contains some of the most massive stars known in our Galaxy, including
the spectacular star Eta Carina. By looking at specific wavelengths
of light emitted by the molecules in the region, we are studying
how the massive stars in the area are impacting on the molecular
cloud from which they formed, and whether this influences subsequent
star formation. The formation process of massive stars (stars >
10 times the mass of our Sun) is still an enigma as their evolution
is so rapid it is hard to observe the full range of activity that
occurs. The Keyhole nebula is a good place to study massive star
formation as it already contains massive stars, clumps that one
day might form stars and lots of gas and dust.
The material in the Keyhole nebula
is highly inhomogeneous and consists of filaments, dark patches
and clumps of dense gas. These features can be seen in optical pictures
of the region (image below left). Of these features, the most interesting
ones are the clumps of material, as these may be at the very earliest
stage of star formation. Some of the clumps are dark, while some
are dark with bright rims. Although optical pictures show a dark
nebula across the region, we are able to see `inside' this by looking
at infra-red light emitted from the region. By turning our infra-red
telescopes towards the Keyhole nebula, we have found that there
are several clumps of gas that are being heated externally by the
nearby massive stars. Comparing then the infra-red pictures with
the optical picture, we found that the clumps with bright-rims are
those which are being heated by the massive stars in the region.
Our observation show that these clumps have been swept up by winds
from Eta Carina, and now weigh about ten times the mass of our Sun.
If these clumps continue to be heated and compressed, they may one
day form stars, revealing the birth process for star formation.
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Image Left
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Three colour optical emission image, courtesy of David
Malin. This image was taken on the Anglo-Australian
Telescope and shows the many features of the region,
including the filaments, bright-rimmed clumps and
dark patches. The star Eta Carina is on the left,
while the Keyhole is the prominent dark patch bisecting
the image.
Image Right
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Infra-red emission from molecular hydrogen showing
the morphology of the `Kangaroo nebula'.
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The morphology of these clumps is interesting,
one of the clumps bears a striking resemblance to a Kangaroo and
has been dubbed the `Kangaroo nebula' (image above right). The velocities
of these clumps have been measured, allowing us to determine the
three dimensional geometry of the cloud (image below). The clumps
appear to be material that has gathered together, pushed out in
all directions by the strong winds from Eta Carina. However, when
a strong stellar wind pushes clumps of gas, we expect to see heating
and a particular type of emission coming from the clumps. We see
no evidence that this is the case, leading to the conclusion that
the winds from Eta Carina have `turned off' and are no longer pushing
the clumps, the clumps appear now to be `coasting' through the nebula.
This scenario is consistent with the properties of Eta Carina, as
it is an unstable star, known to be associated with outbursts and
may even explode as a supernova one day.
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Image left
: A schematic representation
of the three dimensional geometry of the region, based on
our results. The arrows denote the direction in which the
clumps are moving with respect to the nebula. The star Eta
Carina is at the bottom of the nebula.
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A paper with more details of the results
has been submitted to the Monthly Notices of the Royal Astronomical
Society. For more details contact the authors K. J. Brooks, M. G.
Burton, J. M. Rathborne, M. C. B. Ashley and J. W. V. Storey, or
visit the UNSW
Astrophysics home page. For live images of the UNSW instruments
at the South Pole click here.
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Further Information
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