Astronomers have captured four images of the same exploding star nine billion light years away as it performed an incredible cosmic illusion. In doing so, they have confirmed an effect predicted by Albert Einstein's general theory of relativity 100 years ago. The Hubble Telescope snapped the surprising multiple images with the help of a galaxy cluster that acted as a natural magnifying lens. The powerful gravity of a galaxy embedded in a massive cluster of galaxies in this Hubble Space Telescope image is producing multiple images of a single distant supernova far behind it. Both the galaxy and the galaxy cluster are acting like a giant cosmic lens, bending and magnifying light from the supernova behind them . The supernova could be seen because its light took different paths around the cluster located between the exploded star and the Earth-orbiting telescope. The cluster's gravity causes passing photons, or particles of light, to bend. Gravitational lensing occurs when galaxies and other objects amplify the light coming from other distant objects. It enables telescopes like Hubble to see objects that would otherwise be too faint and far away. This will combine the power of Hubble with the natural amplification caused by strong gravitational lensing of distant galaxy clusters to study the past universe. Einstein predicted this when explained how huge objects bend space-time to create what we experience as gravity. Astronomers have been taking advantage of so-called 'gravitational lensing' to boost Hubble's imaging powers and peer farther back in time. They say the latest images could help refine their estimates of the amount and distribution of dark matter in the lensing galaxy. Dark matter cannot be seen directly but is believed to make up most of the universe's mass. By chance, the supernova, which exploded about nine billion years ago, was aligned with the intervening galaxy cluster being used during a Hubble observation period in 2011. Scientists returned to the images in November to look for supernovae and found the quadruple rendering - a configuration known as an Einstein cross. 'The supernova team was looking at these image and bam, up popped not one, not two, not three, but four images,' said astronomer Jennifer Lotz, with the Space Telescope Science Institute in Baltimore, Maryland. 'They were incredibly lucky.' Although astronomers have discovered dozens of multiply imaged galaxies and quasars, they have never seen a stellar explosion resolved into several images . The object has been named Supernova Refsdal in honour of Norwegian astronomer Sjur Refsdal and is the first detected multiply imaged supernova. Astronomers have been taking advantage of so-called 'gravitational lensing' to boost Hubble's imaging powers and peer farther back in time. They say the latest images could help refine their estimates of the amount and distribution of dark matter in the lensing galaxy. The supernova appears in the bottom centre of this image . It appears about 20 times brighter than its natural brightness due to the combined effects of two overlapping lenses, said Jens Hjorth with the Dark Cosmology Center in Denmark. The light from the supernova will fade as the explosion tapers off, but due to additional warping of its light by the galaxy cluster, astronomers expect a re-run. Supernova occur where there is a change in the core of a star. A change can occur in two different ways, with both resulting in a supernova. The first type of supernova happens in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova. The second type of supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. 'The four supernova images captured by Hubble appeared within a few days or weeks of each other and we found them after they had appeared,' Steve Rodney, with Johns Hopkins University. 'But we think the supernova may have appeared in a single image some 20 years ago elsewhere in the cluster field, and, even more excitingly, it is expected to reappear once more in the next one to five years,' he added. 'At that time, we hope to catch it in action.' The supernova's various light paths are analogous to several trains that leave a station at the same time, all traveling at the same speed and bound for the same location. Each train, however, takes a different route, and the distance for each route is not the same, which makes them arrive at different times. Similarly, the supernova images do not appear at the same time because some of the light is delayed by traveling around bends created by the gravity of dense dark matter in the intervening galaxy cluster. 'Our model for the dark matter in the cluster gives us the prediction of when the next image will appear because it tells us how long each train track is, which correlates with time,' said Professor Rodney. Measuring the time delays between images offers clues to the type of warped-space terrain the supernova's light had to cover and will help the astronomers fine-tune the models that map out the cluster's mass. 'We already missed one that we think appeared about 20 years ago, and we found these four images after they had already appeared,' Professor Rodney added. 'The prediction of this future image is the one that is most exciting because we might be able to catch it. We hope to come back to this field with Hubble, and we'll keep looking to see when that expected next image appears.' The galaxy cluster focuses the supernova light along at least three separate paths, and then when one of those light paths happens to be precisely aligned with a single elliptical galaxy within the cluster, a secondary lensing effect occurs. The dark matter associated with the elliptical galaxy refocuses the light into four more paths . Nine billion light-years away, a galaxy's gravity is projecting a distant supernova onto the sky forming what's called an Einstein Cross (shown by the yellow points)
Supernova could be seen because its light took different paths . This allowed astronomers to take four images of the ancient star . A massive galaxy cluster warped the light as it travelled to Earth . Einstein predicted this would happen in his theory which explains how objects bend space-time to create what we experience as gravity . Images could help explain dark matter behaviour in nearby cluster . Light from the supernova is expected to reappear the next few years .