Images of the most distant supernovas ever observed have been captured using a new technique that could provide glimpses of how the earliest galaxies were formed.

Two supernovas that are about 11 billion years old were spotted in a galaxy that would have been one of the first to emerge after the big bang. The technique combined data gathered over four years using the Canada-France-Hawaii Telescope in Hawaii and marks a big advance in detection power.

Professor Jeff Cooke, lead researcher on the study and an astronomer at the University of California, Irvine, said: “The Universe is about 13.7 billion years old, so really we are seeing some of the first stars ever formed.”

Supernovas occur when big stars, usually more than eight times the size of the sun, die then send powerful burning gas into space. Cosmologists usually discover supernovas by comparing pictures of the same area of the sky taken at different times of the year and looking for the appearance of new spots of light, which mark the before and after of a star’s explosion.

In distant galaxies, even the biggest supernovas are too faint to be detected using this method and, until now, astronomers have been confined to looking in the Milky Way and its neighbouring galaxies.

The new technique significantly increases resolution by averaging images of the same piece of sky taken over many nights. In the study, details of which are published in the journal Nature, images were formed using data from eight consecutive six-month periods between 2003 and 2007. About 130 nights of observation went into creating each image.

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

In an image from autumn 2005, bursts of light in two different spots of the sky indicated the presence of supernovas.

The long-term averaging method was previously not possible because large areas of the sky had not been surveyed continually and in sufficient detail. The area of sky studied was about four times the size of the Moon, and only two ancient supernovas were detected in four years of observation data.

The researchers say that by combining even more images the technique could allow even older stars to be spotted. Dr Mark Sullivan, an author on the paper and an astronomer at the University of Oxford, said: “We think this could take us back to around 12 billion years ago.”

The gases thrown out during the earliest supernovas are believed to have “seeded” the Universe with the material that later clumped together to form new stars and galaxies, such as the Milky Way.

By analysing the light from early supernovas, astronomers can determine the chemical elements present in the gases being ejected from the star. Comparing these results with the chemical composition of galaxies today can help to determine the age of galaxies such as the Milky Way.

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