A team of astronomers led by the Australian National University (ANU) has discovered a lens of galactic proportions. Using the Hubble Space Telescope and the Keck Observatory in Hawaii, the scientists saw a supernova not once, but four times by using the gravity of a distant cluster of galaxies to act as a natural lens that magnified and quadrupled the image of the exploding star.

Predicted by Einstein's general theory of relativity, in 1937 it was suggested that a cluster of galaxies would have sufficient mass to bend light and act as a lens tens of millions of light years across by distorting the space-time continuum. In this case, it's a supermassive cluster called MACS J1149.6+2223, which is located more than 5 billion light-years from Earth.

Behind this cluster is Supernova Refsdal, which is in an elliptical galaxy 9.3 billion light-years from Earth and is normally too distant to be observed from our planet. It's a Type 1A supernova that, put simply, is formed by a binary pair of stars where one becomes a white dwarf star and sucks the gas from the companion star until it explodes.

Unlike a glass lens, there's no focal point in a gravitational lens, so the object on the far side of the cluster would appear as a ring or a set of multiple magnified images. In the case of Supernova Refsdal, four images were created in what's known as an Einstein's Cross and the image appears and reappears periodically over decades in a predictable pattern.

How a gravity lens produces multiple images

According to the team, this is the first such phenomenon to be seen in over two decades of searching. It was found by accident by Dr Patrick Kelly from the University of California, Berkeley using archival images from the Hubble telescope and later confirmed by instruments at the Keck observatory in Hawaii.

But the significance of this phenomenon is more than seeing four supernovae for the price of one. The team says that by studying this gravitational lens, it will not only test the theory of relativity, but also allow scientists to measure the cosmic expansion rate, better deduce the distribution of matter in the universe, gain a better understanding of the nature of gravity, and estimate the amount of dark matter and dark energy in the universe.

"It’s perfectly set up, you couldn’t have designed a better experiment," said Brad 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."

The team’s results are published in Science.

The video below discusses viewing a supernova through a gravitational lens.

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