For the first time ever, the Hubble Space Telescope has observed multiple images of a supernova.
The four photos captured by the telescope are in a pattern resembling a cross and are visible thanks to the effects of gravitational lensing.
The concept behind a gravitational lens, originally proposed by Albert Einstein's general theory of relativity, is that matter in clusters of galaxies distributes itself so that it can bend light from sources behind it, creating a magnification of those objects.
In this case, the magnification allowed Hubble to see multiple images of a star undergoing its supernova phase. This is what happens when a star explodes and emits more energy than the sun. This is the final bright phase of a star before it eventually fades and dies.
While looking at Hubble images of galaxy cluster MACS J1149+2223, astronomers noticed the cross of light indicating the supernova. The galaxy in front of the supernova is so great that it's refracting the light of the supernova around it in four distinct areas, creating four images of the same supernova. This is the first time several pictures of such a stellar event have ever been seen.
"The supernova appears about 20 times brighter than its natural brightness," says astronomer Jens Hjorth from the Dark Cosmology Centre, Denmark. "This is due to the combined effects of two overlapping lenses. The massive 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."
Because of this new observation, astronomers can now estimate how much dark matter this galaxy and its cluster contains. Unfortunately, dark matter is completely invisible, so the only evidence of its existence lies with its effects on gravity, with gravitational lensing being one such effect.
However, because of the supernova's distance, it will be visible again, even after the Hubble images of it show it fading out. It will take the supernova's brightness a longer time to reach Earth, so ground-based telescopes will probably pick it up again later.
"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," says Steve Rodney of 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 -- and at that time we hope to catch it in action."
