Due to the gravitational lensing technique, a team of astronomers led by Dr Patrick Kelly from the University of California, Berkeley, has observed four magnified images of a distant exploding star with NASA’s Hubble Space Telescope. The images are arranged around a giant foreground elliptical galaxy embedded in a cluster of galaxies. The arrangement forms a cross-shaped pattern called an Einstein Cross. The powerful gravity from both the elliptical galaxy and its galaxy cluster magnifies the light from the supernova behind them. The galaxy and its galaxy cluster, MACS J1149.6+2223, are 5 billion light-years away from Earth. The supernova is 9.3 billion light-years away.
This image shows four different images of SN Refsdal whose light has been distorted and magnified by the massive galaxy cluster MACS J1149+2223 in front of it. The huge mass of the cluster and one of the galaxies within it is bending the light from a supernova behind them and creating four separate images of the supernova. The light has been magnified and distorted due to gravitational lensing and as a result the images are arranged around the elliptical galaxy in a formation known as an Einstein cross. Image credit: NASA / ESA / S. Rodney, JHU / FrontierSN team / T. Treu, UCLA / P. Kelly, UC Berkeley / GLASS team / J. Lotz, STScI / Frontier Fields team / M. Postman, STScI / CLASH team / Z. Levay, STScI.
The supernova has been named SN Refsdal in honor of Norwegian astronomer Dr Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the Universe.
Although astronomers have discovered dozens of multiply imaged galaxies and quasars, they have never seen a supernova event resolved into several images.
“It really threw me for a loop when I spotted the four images surrounding the galaxy – it was a complete surprise,” said Dr Kelly, who is the first author of the paper published in the journal Science.
While making a routine search of the Grism Lens Amplified Survey from Space’s data, Dr Kelly spotted the four images of SN Refsdal on November 11, 2014.
“This short-lived object was discovered because Dr Kelly very carefully examined the Hubble data and noticed a peculiar pattern. Luck comes to those who are prepared to receive it,” said co-author Prof Alex Filippenko of the University of California, Berkeley.
The supernova appears about 20 times brighter than its natural brightness, due to the combined effects of two overlapping lenses.
The dominant lens is due to the galaxy cluster MACS J1149.6+2223, which focuses the supernova light along at least three separate paths.
A secondary lensing effect occurs when one of those light paths happens to be precisely aligned with a single elliptical galaxy within the cluster.
“The dark matter of that individual galaxy then bends and refocuses the light into four more paths, generating the rare Einstein Cross pattern we are currently observing,” said Dr Steve Rodney of Johns Hopkins University, who is a co-author of the paper.
The enlarged inset view reveals four images of SN Refsdal, spotted in 2014, arranged around a giant elliptical galaxy within the cluster. The light from the supernova passes so closely to the galaxy’s dense core that several light paths are redirected and focused toward Earth. The result is that astronomers see four images that form an Einstein Cross. The blue streaks wrapping around the galaxy are the stretched images of SN Refsdal’s parent spiral galaxy, which has been distorted by the warping of space. Computer models of the cluster predict that another image of the stellar blast will appear within 5 years. The red circle marks the possible location of the next supernova image. Astronomers may have missed an earlier appearance of the supernova in 1995, as marked by the blue circle. These multiple appearances of the exploding star are due to the various paths its light is taking through the maze of clumpy dark matter in the galactic grouping. Each image takes a different route through the cluster and arrives at a different time, due, in part, to differences in the length of the pathways the light follows to reach Earth. Image credit: NASA / ESA / S. Rodney, JHU / FrontierSN team / T. Treu, UCLA / P. Kelly, UC Berkeley / GLASS team / J. Lotz, STScI / Frontier Fields team / M. Postman, STScI / CLASH team / Z. Levay, STScI.
The scientists said that the discovery of SN Refsdal allows not only testing of the Theory of Relativity, but gives information about the strength of gravity, and the amount of dark matter and dark energy in the Universe.
“Because the gravitational effect of the intervening galaxy cluster magnifies the supernova that would normally be too distant to see, it provides a window into the deep past,” said Dr Bradley Tucker of Australian National University, who is the senior author on the study.
“It’s a relic of a simpler time, when the Universe was still slowing down and dark energy was not doing crazy stuff.”
“We can use that to work out how dark matter and dark energy have messed up the Universe.”
The astronomers said that when SN Refsdal’s images do fade away, they will have a rare chance to catch a rerun of the supernova.
This is because the current four-image pattern is only one component of the lensing display.
SN Refsdal may have appeared in a single image some 20 years ago elsewhere in the cluster field, and it is expected to reappear once more in the next 1 – 5 years.
The prediction of a future appearance is based on computer models of the cluster, which describe the various paths the divided light is taking through the maze of clumpy dark matter in the galactic grouping.
Each image takes a different route through the cluster and arrives at a different time, due, in part, to differences in the length of the pathways the light follows to reach Earth.
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Patrick L. Kelly et al. 2015. Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens. Science, vol. 347, no. 6226, pp. 1123-1126; doi: 10.1126/science.aaa3350
