University of Toronto astronomer part of team that finds new way to study supernovae

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Courtesy of the Department of Astronomy & Astrophysics, University of Toronto

An international team of astronomers has found a better way to examine the origins and evolution of galaxies that form following supernova explosions – the starting point for the formation of galaxies when a star explodes – and they have discovered new supernovae in the process. "We've devised a technique to discover supernova explosions at greater distances than previously known," says team member Ray Carlberg of U of T's Department of Astronomy and Astrophysics. "The most distant one occurred during the time when galaxies were at their peak phase of star formation activity, approximately 10 billion years ago, twice the age of Earth."

The ultra-distant supernovae were discovered in images acquired as part of the Canada-France-Hawaii Telescope Legacy Survey. "Our trick was to add together six months of images to create a very deep image of the sky," says Carlberg. "This allows us to look for objects that changed in brightness over a long period of time," says Carlberg of their ability to measure the changing intensity of light emitted by cosmic debris following a supernova explosion. "The specific type of supernovae we discovered have bright light emission lines even after the original explosion has faded away, "says Carlberg. "This emission is a result of the supernova explosion colliding with unusually dense gas around the exploding star. Future studies of the line intensities will reveal the ongoing development of the explosion and give information about the chemical composition of the gas at this early time."

The discovery opens a new avenue to study the details of how galaxies and their components evolve with time. "During a supernova explosion, virtually all of the elements heavier than oxygen – calcium, silicon, iron, all the way to up uranium – are produced," says Carlberg. "These metals, along with the tremendous blast of energy they release into the surrounding gas, make supernovae of great interest for studying the build up of the galaxy and its component stars, and even the rocky planets like our own."

A report on the discovery appears in the July 9 issue of Nature. In addition to Carlberg, a fellow of the Canadian Institute for Advanced Research, contributors to the study included Jeff Cooke, Elizabeth J. Barton, James S. Bullock and Erik Tollerud of the University of California, Irvine, Mark Sullivan of the University of Oxford, and Avishay Gal-Yam Weizmann Institute of Science in Israel. Funding was provided by the Gary McCue Postdoctoral Fellowship and the Centre for Cosmology at the University of California, Irvine, the Natural Sciences and Engineering Research Council of Canada, and the Royal Society.

Source: University of Toronto