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Dazzling supernova mystery solved | |
(about 20 hours later) | |
An exceptionally bright supernova that baffled scientists has been explained. | An exceptionally bright supernova that baffled scientists has been explained. |
It is so luminous because a galaxy sitting in front amplifies its light - making it appear 100 billion times more dazzling than our Sun. | It is so luminous because a galaxy sitting in front amplifies its light - making it appear 100 billion times more dazzling than our Sun. |
This cosmic magnifying glass lay hidden between Earth and the supernova - and has now been detected with a telescope in Hawaii. | This cosmic magnifying glass lay hidden between Earth and the supernova - and has now been detected with a telescope in Hawaii. |
The discovery, reported in the journal Science, settles an important controversy in the field of astronomy. | The discovery, reported in the journal Science, settles an important controversy in the field of astronomy. |
In 2010, a team of scientists observed the supernova, PS1-10afx, shining 30 times brighter than any other in its class. | In 2010, a team of scientists observed the supernova, PS1-10afx, shining 30 times brighter than any other in its class. |
They concluded it was a completely new type of stellar explosion. | They concluded it was a completely new type of stellar explosion. |
But while there are a few, rare supernovas that have been found with comparable luminosities, there was something odd about this one, according to Dr Robert Quimby of the University of Tokyo's Kavli Institute. | But while there are a few, rare supernovas that have been found with comparable luminosities, there was something odd about this one, according to Dr Robert Quimby of the University of Tokyo's Kavli Institute. |
"PS1-10afx was different in just about every way. It evolved too fast, its host galaxy is too big, and it was way, way too red," he explained. | "PS1-10afx was different in just about every way. It evolved too fast, its host galaxy is too big, and it was way, way too red," he explained. |
His team had another idea. They ventured that PS1-10afx was a normal Type Ia supernova magnified by a lens in the form of a massive object, such as supermassive black hole, nearby. | His team had another idea. They ventured that PS1-10afx was a normal Type Ia supernova magnified by a lens in the form of a massive object, such as supermassive black hole, nearby. |
The only problem: "We had no direct evidence for the lens," said Dr Quimby. | The only problem: "We had no direct evidence for the lens," said Dr Quimby. |
"Thus [our] explanation required a bit of magic... and scientists don't generally buy into magic." | "Thus [our] explanation required a bit of magic... and scientists don't generally buy into magic." |
However, he reasoned that if there was a gravitational lens magnifying the supernova, this lens would still be there today - even though the supernova has faded away. | However, he reasoned that if there was a gravitational lens magnifying the supernova, this lens would still be there today - even though the supernova has faded away. |
To find it, his team used the Keck telescope in Hawaii to observe PS1-10afx's host galaxy. | To find it, his team used the Keck telescope in Hawaii to observe PS1-10afx's host galaxy. |
"Looking at the spectra we could check to see if there was light coming from two sources at two separate distances, which is what we found," said Dr Quimby. | "Looking at the spectra we could check to see if there was light coming from two sources at two separate distances, which is what we found," said Dr Quimby. |
"There is a second, previously unidentified galaxy, hiding in plain sight in front of the supernova." | "There is a second, previously unidentified galaxy, hiding in plain sight in front of the supernova." |
The lens galaxy was missed previously because its light was lost in the bright glare of the supernova, the authors say. | The lens galaxy was missed previously because its light was lost in the bright glare of the supernova, the authors say. |
"Although the lens galaxy is closer to us, it appears fainter because it has older stars that, like flashlights with old batteries, don't shine as bright," said Dr Quimby. | "Although the lens galaxy is closer to us, it appears fainter because it has older stars that, like flashlights with old batteries, don't shine as bright," said Dr Quimby. |
The Universe was almost a billion years younger when the supernova exploded than when its light rays were bent by the foreground lens. | The Universe was almost a billion years younger when the supernova exploded than when its light rays were bent by the foreground lens. |
"Although this warping of space time probably created four separate images of the supernova when viewed from Earth, we find that these likely appeared as a single source after atmospheric blurring," said Dr Quimby. | "Although this warping of space time probably created four separate images of the supernova when viewed from Earth, we find that these likely appeared as a single source after atmospheric blurring," said Dr Quimby. |
The discovery could provide astronomers with a new tool to measure the expansion of the Universe. | The discovery could provide astronomers with a new tool to measure the expansion of the Universe. |
That's because PS1-10afx is the first supernova of its kind to be magnified by "strong gravitational lensing" - where multiple images of the supernova are formed - creating the extra-bright appearance. | That's because PS1-10afx is the first supernova of its kind to be magnified by "strong gravitational lensing" - where multiple images of the supernova are formed - creating the extra-bright appearance. |
"Each image will arrive at a different time with the exact delay dependent on how fast the Universe is expanding. In principle, measuring this delay provides a direct way to measure cosmic expansion," Dr Quimby explained. | "Each image will arrive at a different time with the exact delay dependent on how fast the Universe is expanding. In principle, measuring this delay provides a direct way to measure cosmic expansion," Dr Quimby explained. |
Unfortunately, the scientists could not do this with PS1-10afx because it faded away before its importance was recognised. But now they know what to look for. | Unfortunately, the scientists could not do this with PS1-10afx because it faded away before its importance was recognised. But now they know what to look for. |
"Our discovery implies there are many more gravitationally lensed supernovae that are barely resolved, like PS110afx," said Prof Masamune Oguri, of the University of Tokyo. | "Our discovery implies there are many more gravitationally lensed supernovae that are barely resolved, like PS110afx," said Prof Masamune Oguri, of the University of Tokyo. |
"Our selection method can soon be applied to future surveys to improve our understanding of the expanding Universe." | "Our selection method can soon be applied to future surveys to improve our understanding of the expanding Universe." |
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