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 The four images captured by Hubble were caused by light taking
different paths around a massive galaxy cluster located between the
exploded star and the Earth-orbiting telescope.
The cluster’s gravity causes passing photons, or particles of light,
to bend, a phenomenon predicted 100 years ago by physicist Albert
Einstein.
Astronomers have been taking advantage of so-called “gravitational
lensing” to boost Hubble’s imaging powers and peer farther back in
time. By chance, the supernova, which exploded about 9 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.”
The object, known as Supernova Refsdal in honor of Norwegian
astronomer Sjur Refsdal, is the first detected multiply imaged
supernova. 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.
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"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, said in a
statement.
"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 research appears in this week's issue of the journal Science.
(Reporting by Irene Klotz; Editing by Tom Brown)
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