Astronomers have turned up the oldest and most distant supernova ever found: the star that created it detonated just 3 billion years after the big bang. The technique used to find it could reveal tens of thousands of other ancient supernovae, tracing out how the universe became seeded over time with heavy elements.

Because light travels at a finite speed, more distant supernovae also occur further back in time. The calculated distance of the newly discovered blast suggests it occurred 10.7 billion years ago – about 1.5 billion years earlier than the previous record holder.

The new blast was a 'type II' supernova, which detonated when a star 50 to 100 times as massive as the sun ran out of nuclear fuel and could no longer support its own weight.

This supernova is classified as a 'type IIn' supernova, which is caused by a star that belches out large quantities of gas before its final explosion. Its fiery death heats up that gas, causing it to glow long after light from the blast itself has faded. Indeed, the light from type IIn supernovae lasts for years, while ordinary supernovae may be visible for just a few weeks.

The long-lived light show allowed a team led by Jeff Cooke of the University of California, Irvine, to find the supernova in images taken by the Canada-France-Hawaii Telescope Legacy Survey, a project that imaged the same four patches of sky over a period of five years using a 3.6-metre telescope in Hawaii.

Chemical history

The researchers added up a number of images from different nights to create deeper, more sensitive pictures of the early universe. Then they compared the resulting images from year to year in search of galaxies that seemed to brighten.

0905N_SUPERNOVA_narrowweb__300x386,0Cooke, who has analysed just a fifth of the survey data, expects more ancient supernovae to be found in the project.

If they are, the explosions would shed light on how the universe became seeded with heavier elements. Only a few lightweight elements – hydrogen, helium, and lithium – are thought to have been created in the big bang; all others were forged over time in the nuclear furnaces of stars and in supernovae.

Since the spectrum of light from a supernova reveals the chemical composition of the exploding star, observing many such explosions would allow astronomers to trace out a chemical history of the universe.

Earliest stars

Future studies should also turn up supernovae from the early universe. These include surveys that could be conducted with a camera now under development for the 8.2-metre Subaru telescope in Hawaii and with NASA's 6.5-metre James Webb Space Telescope, which is set to launch in 2013.

"Using this method, we should be able to see objects much farther away and therefore much farther back in time, and actually see some of the first stars that ever lived," Cooke told New Scientist.

Light from one of the first stars may already have been found with the discovery earlier this year of a gamma-ray burst that exploded when the universe was less than 650 million years old. Such bursts are thought to be caused by high-speed jets of matter spewed out of massive stars when they die.

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