Astronomers have glimpsed a far off and ancient star exploding, not once, but four times.

The exploding star, or supernova, was directly behind a cluster of huge galaxies, whose mass is so great that they warp space-time. This forms a cosmic magnifying glass that creates multiple images of the supernova, an effect first predicted by Albert Einstein's General Theory of Relativity 100 years ago.

Dr Brad Tucker from The Australian National University (ANU) says it's a dream discovery for the team.

"It's perfectly set up, you couldn't have designed a better experiment," said Dr Tucker, from ANU Research School of Astronomy and Astrophysics.

"You can test some of the biggest questions about Einstein's theory of relativity all at once - it kills three birds with one stone."

Astronomers have mounted searches for such a cosmic arrangement over the past 20 years. However, this discovery was made during a separate search for distant galaxies by Dr Patrick Kelly from University of California, Berkeley.

"It really threw me for a loop when I spotted the four images surrounding the galaxy - it was a complete surprise," he said.

The lucky discovery allows not only testing of the Theory of Relativity, but gives information about the strength of gravity, and the amount of dark matter and dark energy in the universe.

Because the gravitational effect of the intervening galaxy cluster magnifies the supernova that would normally be too distant to see, it provides a window into the deep past, Dr Tucker said.

"It's a relic of a simpler time, when the universe was still slowing down and dark energy was not doing crazy stuff," he said.

"We can use that to work out how dark matter and dark energy have messed up the universe."