The new 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. Light from the exploding stars, or supernovae, began its journey to Earth 11 billion years ago, not long after the "Big Bang" that created the cosmos. The next furthest large supernova known is six billion light years away. Professor Jeff Cooke, lead researcher on the study and an astronomer at the University of California, Irvine, found four supernovae, including the two distant objects, after analysing images from the Canada-France-Hawaii Telescope in Hawaii. "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.

Cooke, who has analysed just a fifth of the survey data, expects more ancient supernovae to be found in the project. 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. 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. According to the new research, which is reported in the journal Nature, the new technique involves blending together pictures taken over the course of a year, and comparing them with image compilations from other years. "If you stack all of those images into one big pile, then you can reach deeper and see fainter objects. It's like in photography when you open the shutter for a long time. You'll collect more light with a longer exposure," Cooke said. He said the universe is about 13.7 billion years old, "so really we are seeing some of the first stars ever formed".

Along with his colleagues, last year Cook had discovered an early-stage cluster of galaxies 11.4 billion light years away, the most distant ever detected. 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, the New Scientist reported.