Images of star exploding four times captured by astronomers

Australian researchers were among a team that captured images of the same star exploding four times, thanks to its location behind a massive cluster of galaxies.

The gravitational pull of the galaxies meant light and time were bent around them, creating a cosmic magnifying glass in a process known as gravitational lensing, which was first predicted by Albert Einstein’s theory of relativity. This magnified the supernova, which at 9.3bn light years away would have been too distant for the Hubble space telescope to detect were it not for this lensing effect.

Co-author of a paper from the Australian National University, Dr Brad Tucker, said it was the first time such an explosion had been captured multiple times.

Computer modelling suggested that the researchers missed opportunities to see the supernova 50 years ago and again 10 years ago, but the images would likely repeat in five years, the study published in the international journal Science on Friday said.

“It means we can wait for these appearances to replay over time and measure directly how much space has grown in that intervening time,” Tucker said. “The other exciting aspect of this discovery is that while we know the universe is accelerating, it hasn’t always been. It slowed down before it sped up.

“We found this star travelled through the period where the universe was moving from slowing down to speeding up, and we can now probe this part of the universe which we currently don’t have many measurements for.”

The first gravitational lens was discovered in 1979 and since then, astronomers have discovered the universe is filled with them. While it was predicted that a supernova could be gravitationally lensed, Tucker and his colleagues provided the first example of it.

“It’s a relic of a simpler time, when the universe was still slowing down and dark energy was not doing crazy stuff,” Tucker said. “We can use that to work out how dark matter and dark energy have messed up the universe.”

The study, which also involved the University of Melbourne, was led by astronomer Dr Patrick Kelly from the University of California in the US. Kelly discovered the lensed supernova in November last year by luck, while looking for interesting explosions during separate research.

“We can get magnifications of up to 100 times by looking through these galaxy clusters,” Kelly said. “By luck, we have been able to follow it very closely in all four images, getting data every two to three days.”