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
U of T Public Affairs