Stars in Their Eyes

A team of astronomers, including Dr Brad Tucker from the ANU Research School of Astronomy and Astrophysics, have captured a 9.3 billion year old explosion four times in a single photograph. The achievement is described in their paper “Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens”, published in Science.

The exploding star, called a supernova, was directly behind a cluster of galaxies so large its mass significantly warps space-time, an effect called gravitational lensing. This formed a “magnifying glass” that created multiple images of the supernova. This effect was predicted by Einstein’s General Theory of Relativity almost 100 years ago, but it had not been used to observe a supernova until now.

It lets astronomers do this for two different reasons. Firstly, the aforementioned “magnifying glass” effect. This supernova was so far away that we normally wouldn’t be able to see it as it would be too faint. But as the galaxy cluster was perfectly positioned to refocus the light towards us we were able to detect it.

Secondly, because different areas of space are full of different things, by comparing the different images astronomers can test our understanding of the universe. For example, since images of the same supernova began to appear several days or weeks apart from each other, the light must have travelled different distances. By comparing these measured differences with the expected differences the size and expansion of the universe can be analysed. In addition, by examining the galaxy cluster we can predict when we expect more light from the supernova to become visible and further test our understanding of the universe.

Dr Tucker says it’s a very lucky discovery. “It’s perfectly set up, you couldn’t have designed a better experiment. You can test some of the biggest questions about Einstein’s theory of relativity all at once – it kills three birds with one stone.”[1]

This discovery allows testing of the Theory of Relativity, the strength of gravity and the extent of dark matter and dark energy that could be out there “messing up” the universe, as Dr Tucker put it.

When asked about his role in the discovery, Dr Tucker elaborated that he has been tasked with trying to get the light spectrum of the supernova. This information would have allowed the team to figure out exactly what type of star and supernova it was, as well as how far away it was from the Earth. They tried using the 10 metre Keck telescope in Hawaii to do this. While they couldn’t figure out the type of supernova, they did find out how far away it is: 9.3 billion light years.

But Dr Tucker wasn’t concerned about not knowing the type – they’ll just have to try again. And they plan to do just that very soon.


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