This artist’s impression of a supernova shows the layers of gas ejected prior to the final deathly explosion of a massive star. CREDIT:NASA/Swift/Skyworks Digital/Dana Berry This image was taken with CFHT as part of the telescope’s Legacy Survey and shows one of the deep fields used to find the most distant supernovae to date. CREDIT: Jeff Cooke/CFHT This image, shows the host galaxy containing one of the newly discovered supernovae. It subtracts the images from the years that the supernova was not detected as well as the galaxy’s light to reveal only the supernova. CREDIT: Jeff Cooke/CFHT

July 8, 2009 - Mauna Kea, Hawaii

Science conducted from the summit of Mauna Kea on the Big Island of Hawaii has again rewritten the record books, this time for the discovery of the most distant supernovae.

A team using W. M. Keck Observatory and Canada-France-Hawaii Telescope (CFHT) has identified remnants of two massive stars that exploded roughly 11 billion years ago. Prior to this discovery, astronomers’ records showed that the most distant supernova of this type exploded roughly six billion years ago, and the most distant of any supernovae type exploded roughly nine billion years ago.

"Studying the deaths of these early stars is essential to understanding the evolution of the Universe and how its elements were formed and distributed to create later stars and even planets," said cosmologist Jeff Cooke of the University of California, Irvine.

The team used a ground breaking new method to study the explosive death of stars. Astronomers examined archival data from the CFHT Legacy Survey to identify four, extremely distant objects that appeared to brighten and then fade over time, resembling distant supernovae. The team stacked and blended a year’s worth of CFHT images taken of the same, dark patch of sky and did this for four separate years. Stacking the images into one composite enabled the team to detect fainter objects and thereby probe farther back in the Universe.

After identifying four potential supernovae, the astronomers used the Low Resolution Imaging Spectrograph (LRIS) on the Keck I telescope and the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope to analyze the spectrum of light that each object emitted to determine the objects’ composition and distance.

Cooke’s technique has received praise from colleagues. "It’s simple, clean and the results are unambiguous. In retrospect, I can’t believe we haven’t capitalized on this method sooner,” said astronomer Alicia Soderberg, who studies supernovae at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Cooke also said that although the newly identified explosions may be the farthest of any supernovae type found to date, the innovative method developed to identify the explosions should make it possible to discover even more distant supernovae — possibly even a few of the very first stars to blow themselves apart.

Both the results and the new method appear in the July 9 edition of Nature.