November 22, 2005


            The genius of Albert Einstein, who added a "cosmological
constant" to his equation for the expansion of the universe
but later retracted it, may be vindicated by new research.

            The enigmatic dark energy that drives the accelerating
expansion of the universe behaves just like Einstein's famed
cosmological constant, according to the Supernova Legacy
Survey (SNLS), an international team of researchers in France
and Canada that collaborated with large telescope observers at
Oxford, Caltech and Berkeley. Their observations reveal that
the dark energy behaves like Einstein's cosmological constant
to a precision of 10 per cent.

"The significance is huge," said Professor Ray Carlberg of the Department
of Astronomy and Astrophysics at U of T. "Our observation is at odds with
a number of theoretical ideas about the nature of dark energy that predict
that it should change as the universe expands, and as far as we can see,
it doesn't." The results will be published in an upcoming issue of the
journal Astronomy & Astrophysics.

"The Supernova Legacy Survey is arguably the world leader in our quest to
understand the nature of dark energy," said study co-author Chris
Pritchet, a professor of physics and astronomy at the University of
Victoria in British Columbia, Canada.

            The researchers made their discovery using an innovative,
340-million pixel camera called MegaCam, built by the 
Canada-France-Hawaii Telescope and the French atomic energy
agency, Commissariat à l'Énergie Atomique. "Because of its
wide field of view (you can fit four moons in an image) it
allows us to measure simultaneously, and very precisely,
several supernovae, which are rare events," said Pierre
Astier, one of the scientists with the Centre National de la
Recherche Scientifique (CNRS) in France.

"Improved observations of distant supernovae are the most immediate way in
which we can learn more about the mysterious dark energy," adds Richard
Ellis, a professor of astronomy at the California Institute of Technology.
"This study is a very big step forward in quantity and quality."

            Study co-author Saul Perlmutter, a physics professor at the
University of California, Berkeley, says the findings kick off
a dramatic new generation of cosmology work using supernovae.
"The data is more beautiful than we could have imagined 10
years ago -- a real tribute to the instrument builders, the
analysis teams and the large scientific vision of the Canadian
and French science communities."

The SNLS is a collaborative international effort that uses images from the
Canada-France-Hawaii Telescope, a 3.6-metre telescope atop Mauna Kea, a
dormant Hawaiian volcano. The current results are based on about 20 nights
of data, the first of over nearly 200 nights of observing time for this
project. The researchers identify the few dozen bright pixels in the 340
million captured by MegaCam to find distant supernovae, then acquire their
spectra using some of the largest telescopes on earth: the Frederick C.
Gillett Gemini North Telescope on Mauna Kea, the Gemini South Telescope on
the Cerro Pachón mountain in the Chilean Andes, the European Southern
Observatory Very Large Telescopes (VLT) at the Paranal Observatory in
Atacama, Chile, and the Keck telescopes on Mauna Kea. The SNLS is one
component of a massive 500-night program of imaging being undertaken as
the CFHT Legacy Survey.

"Only the world's largest optical telescopes, those from eight to 10
metres in diameter, are capable of studying distant supernovae in detail
by examining the spectrum," said Isobel Hook, an astronomer in the
Department of Astrophysics at Oxford University.

The current paper is based on about one-tenth of the imaging data that
will be obtained by the end of the survey. Future results are expected to
double or even triple the precision of these findings and conclusively
solve several remaining mysteries about the nature of dark energy.

 The research was funded by the Canada-France-Hawaii Telescope, the
Commissariat à l'Énergie Atomique (CEA), Centre National de la Recherche
Scientifique, Institut National des Sciences de l'Univers du CNRS, the
Natural Sciences and Engineering Research Council of Canada, the National
Research Council of Canada's Herzberg Institute of Astrophysics, the
Gemini Observatory, the Particle Physics and Astronomy Research Council,
the W. M. Keck Observatory and the European Southern Observatory.

The University of Toronto is Canada's leading teaching and research
university and aims to be among the world's best. For eleven consecutive
years, U of T has taken the top spot among medical/doctoral universities
in the annual Maclean's magazine university ranking. With more than 70,000
students, U of T comprises 28 divisions, colleges and faculties on three
campuses. This includes 14 professional faculties, nine fully-affiliated
teaching hospitals, numerous research centres and Canada's largest
university library system -- the third largest in North America.

Professor Ray Carlberg
Department of Astronomy and Astrophysics

Nicolle Wahl
U of T Public Affairs

Professor Chris Pritchett
University of Victoria
(250) 721-7715