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by Margaret Milne
Astronomers
were shocked in 1998 when they realized the universe was dominated
by a mysterious energy that was forcing galaxies apart from each
other. Four years later, the nature of this “dark energy”
is still unknown, but Dr. Chris Pritchet of UVic’s physics
and astronomy department hopes to change that.
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Pritchet |
Pritchet is coordinator of the UltraDeep Survey,
based at the Canada France Hawaii Telescope (CFHT) on Mauna Kea,
Hawaii. For 202 nights over the next five years, the telescope will
take pictures of more than 2,000 supernovae—the powerful explosions
that herald the death of stars. Analysing these supernovae will
allow Pritchet and his international collaborators to make the first
precise measurement of the nature of dark energy.
Understanding dark energy will help astronomers
better understand why and how mass and energy exist.
Although no one is sure what causes dark energy,
astronomers know what it does—it fills the universe and exerts
a repulsive force, making galaxies travel faster and faster as they
move away from each other with the expansion of the universe. The
existence of dark energy was first noticed by astronomers studying
far-off supernovae.
“The very distant supernovae were fainter
than they should be,” says Pritchet. This showed that distant
objects were further away than expected—they had been forced
away by dark energy.
The UltraDeep Survey will take pictures of supernovae as distant
as 30 billion light years, and create the world’s largest sample
of supernova observations. With so many supernovae to examine, astronomers
can search for subtle patterns in the data that will allow them
to choose between competing theories for the cause of dark energy.
One reason the UltraDeep Survey is unrivalled
is that it will use MegaCam, the world’s largest digital camera.
“It’s just like the digital cameras you can buy at a store,
but a thousand times larger,” says Pritchet. MegaCam will be
attached to the CFHT telescope, renowned for images of exquisite
quality. “With this combination,” says Pritchet, “we’re
miles ahead of everyone else.”
To automate the search for supernovae, the UltraDeep Survey team
will use a series of computer programs known as a pipeline. “The
input to the pipeline is data from the tele-scope,” says Pritchet.
“The output is a list of potential supernovae.” One of
his jobs as co-ordinator is to design the pipeline.
Pritchet will be working with Dave Balam, a research
associate in UVic’s astronomy group. Graduate students and
post-doctoral fellows will also have a chance to contribute. “They
see we’re excited about this project, and that excitement trickles
down. After all, we’re working on the largest scale of all—the
origin and evolution of the universe. You don’t get any larger
than that.”
He points to a cartoon on his door, where a white-coated
scientist wonders if there’s more to life than unlocking the
secrets of the universe. “There’s not,” says Pritchet.
“There are various ways to do it—poetic, spiritual, scientific.
We’ve chosen the scientific approach.”
- The UltraWide Survey may seem like an ambitious project …
But actually, it’s only one part of a
larger undertaking. For the next five years, Canadian and French
astronomers will spend 450 nights at the Canada France Hawaii Telescope
(CFHT), taking images for the Telescope Legacy Survey.
- The project has three related components. The
UltraDeep Survey will use supernovae to study dark energy. The Deep
Survey will make maps of invisible “dark matter” by studying
how it bends the light of distant galaxies. And the UltraWide Survey
will find more than 1,000 Kuiper Belt Objects,
the leftovers from the formation of our solar system.
- Every astronomer working in Canada or France will
have the opportunity to join the project and use the data. A steering
group will oversee the operation of the project. Pritchet is a member
of this group; other Canadian members include Dr. Ray Carlberg at
the University of Toronto, and Drs. J.J.
Kavelaars and David Schade, both based at the Dominion Astrophysical
Observatory in Victoria.
- The survey project is supported by the Centre
National de la Recherche Scientifique and the Institut National
des Sciences de l’Univers in France, the Canada France Hawaii
Telescope, and the National Research Council and the Natural Sciences
and Engineering Research Council of Canada.
- Pritchet and his collaborators are going to take
a lot of pictures. The CFHT Legacy Survey project,
which includes the UltraDeep Survey, will create about 2,000 images,
and each image will need nearly one gigabyte of memory to store.
In total, they’re going to produce the equivalent of more than
200,000 filing cabinet drawers full of information.
- The task of dealing with all this data falls to the Canadian
Astronomy Data Centre (CADC). Inconspicuously tucked away on the
slopes of Little Saanich Mountain, the CADC is one of the world’s
major astronomy data clearinghouses.
- The CADC started in 1986 as one of three worldwide centres
for distributing images from the
Hubble Space Telescope. It now archives all the scientific data
produced by CFHT, as well as providing access to many other international
astronomical databases.
In addition to storing and distributing data, the scientists
of the CADC also develop computer programs to help astronomers access
information more easily and intelligently.
- The head of the CADC is Dr. David Schade, a UVic alumni.
Other UVic graduates also work for the CADC, and co-op students
have spent work terms at the centre.
 Margaret
Milne wrote this as a participant in the SPARK program (Students
Promoting Awareness of Research Knowledge), funded by UVic, the
Natural Sciences and Engineering Research Council, and the Social
Sciences and Humanities Research Council.
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