July 9, 2009 -- After combing through years of archival
images of distant galaxies, astronomers have found the exploded remains of a
star that is about 11 billion light years from Earth, the most distant supernova
found to date.
The discovery, reported in this week's Nature, promises to open the
early universe to greater scrutiny in an ongoing effort to understand how
galaxies form and evolve.
The type of supernovae found by University of California-Irvine astronomer
Jeff Cooke and colleagues can serve as a beacon, because the supernovae not only
explode with a brilliant flash of light, but also illuminate shells of gas that they
have been shedding for years before their violent deaths.
When a star explodes, ejected material rams into surrounding gas
shells, causing them to glow. Unlike the explosion, which is relatively
short-lived, the glowing gas shells radiate for years.
That gave Cooke and colleagues an opportunity to verify their findings, which
were drawn from analysis of imagery from the Canada-France-Hawaii Telescope
Legacy Survey. The team selected about 60,000 target galaxies and combined the
light collected during six months of near-daily observations. They then compared
that result with data compiled from a six-month period of another year.

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Four targets showed brightening over time, perhaps due to supernovae explosions. Cooke then used the Keck Telescope to
look for the glowing shell remains for verification.
"In retrospect, I can't believe we haven't capitalized on this method
sooner," said astronomer Alicia Soderberg, with the Harvard-Smithsonian Center
for Astrophysics in Cambridge, Mass.
Cooke plans to continue combing archived images -- he's only about one-fifth
of the way through the archival images -- to look for additional distant
supernovae. Eventually, with more powerful telescopes, he hopes to obtain the
chemical fingerprints of the exploded remains to determine if stars forming in
very young galaxies were made of different materials than stars born in
later-generation galaxies.
Astronomers believe that heavier elements were made in stars and then
distributed in space to become raw materials for future galaxies.
"We should be able to do this when the supernovae is much brighter and
measure metal content," said Ray Carlberg with the University of Toronto.
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