July 8, 2009

Scientists Discover Farthest Supernovae To Date

Cosmologists have discovered two massive supernovae farther away than ever before using a new technique that could shed light on the formation of galaxies as well as how the Earth was formed.

"We've devised a technique to discover supernova explosions at greater distances than previously known," said Ray Carlberg of the University of Toronto'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 international team of cosmologists discovered the supernovae as part of the Canada-France-Hawaii Telescope Legacy Survey. Their findings are reported in the July 9 issue of the journal Nature.

The team discovered the giant supernovae which occurred 11 billion years ago. The most distant previous discovery occurred about 6 billion years ago.

"During a supernova explosion, virtually all of the elements heavier than oxygen "“ calcium, silicon, iron, all the way to up uranium "“ are produced," said 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."

Traditionally, such discoveries are made by searching for a new light in comparing pictures taken different times of the same swath of sky.

Jeff Cooke, McCue Postdoctoral Fellow in physics and astronomy, said the team added the collection of images onto each other and compared them to image compilations from other years.

"If you stack all of those images into one big pile, then you can reach deeper and see fainter objects," Cooke said. "It's like in photography when you open the shutter for a long time. You'll collect more light with a longer exposure."

"The universe is about 13.7 billion years old, so really we are seeing some of the first stars ever formed," he added.

"Our trick was to add together six months of images to create a very deep image of the sky," said Carlberg. "This allows us to look for objects that changed in brightness over a long period of time."

"The specific type of supernovae we discovered have bright light emission lines even after the original explosion has faded away."

"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."


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