The explosive deaths of two massive stars roughly 11 billion years ago have been identified by astronomers using the Keck Observatory and Canada-France-Hawaii Telescopes on Mauna Kea.

They are the most distant and oldest deaths of early stars found in the universe, astronomers reported in today's issue of the journal Nature.

“;The universe is about 13.7 billion years old, so really we are seeing some of the first stars ever formed,”; said cosmologist Jeff Cooke of the University of California, Irvine.

A supernova occurs when a massive star more than eight times the mass of the sun dies in a powerful, luminous explosion.

Studying the most distant supernovae “;is essential to understanding the evolution of the universe and how its elements were formed and distributed to create later stars and even planets,”; Cooke said in a Keck Observatory news release.

He developed a new technique to study supernovae that are roughly 50 to 100 times the mass of the sun. The method may eventually find the first deaths of stars in the universe, he said.

The cosmologists examined archival data from the Canada-France-Hawaii Telescope Legacy Survey to find the most distant supernovae. About 2,000 supernovae were monitored in the five-year survey to study the distribution of matter in the universe and its evolution.

The scientists stacked and blended images taken of the same piece of sky over four years into one composite, enabling them to detect fainter objects and go further back in the universe.

“;It's like in photography when you open the shutter for a long time,”; Cooke said. “;You'll collect more light with a longer exposure.”;

Comparing composite images, the astronomers identified four extremely distant objects that appeared to brighten, then fade over time, resembling distant supernovae.

Cooke looked at the spectrum of light from each object with the Keck telescope and confirmed they were supernovae. The data showed the light had traveled nearly 11 billion light years to reach Earth, he said.

Before his team's discovery, records showed the most distant supernova of the type they detected exploded roughly 6 billion years ago, and the most distant of any type of supernovae exploded about 9 billion years ago.