Gravitational Lensing (Cosmic magnifying glass)

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News:

http://www.iflscience.com/space/gravitational-lens-allows-us-witness-supernova-repeat

Four versions of the same supernova explosion have been captured because a large galaxy between us and the event is distorting the path on which the light travels to reach us. The event not only makes visible a supernovae more distant than we normally see but provides the opportunity astronomers have been dreaming of to test three of the biggest questions in cosmology. Even more opportunities should arise in future.

One of the key predictions of General Relativity is that mass bends spacetime, and therefore light. Einstein predicted that very massive objects could focus light in a manner analogous with glass lenses, an effect finally observed in 1979.

Depending on the locations of the relevant objects we often see multiple images of the same distant quasar or galaxy. Since this light follows different paths to reach us the distance traveled on each will not be identical, so we are seeing some slightly delayed relative to the others. This makes little difference for an object whose brightness barely varies.

However, in 1964 Sjur Refsdal pointed out that different images of the same supernova would capture different moments in the explosion’s evolution, and might be used to test the rate at which the universe is expanding. Great efforts have been made to find such an example of such a valuable case. Dr Patrick Kelly of the University of California, Berkeley was looking for distant galaxies and came across the sight of four images of a nine billion year old supernova around a galaxy in the MACS J1149.6+2223 cluster.

Astronomers have glimpsed a far off and ancient star exploding, not once, but four times.

The exploding star, or supernova, was directly behind a cluster of huge galaxies, whose mass is so great that they warp space-time. This forms a cosmic magnifying glass that creates multiple images of the supernova, an effect first predicted by Albert Einstein’s General Theory of Relativity 100 years ago.

Dr Brad Tucker from The Australian National University (ANU) says it’s a dream discovery for the team.

“It’s perfectly set up, you couldn’t have designed a better experiment,” said Dr Tucker, from ANU Research School of Astronomy and Astrophysics.

“You can test some of the biggest questions about Einstein’s theory of relativity all at once – it kills three birds with one stone.”

Astronomers have mounted searches for such a cosmic arrangement over the past 20 years. However, this discovery was made during a separate search for distant galaxies by Dr Patrick Kelly from University of California, Berkeley.

“It really threw me for a loop when I spotted the four images surrounding the galaxy – it was a complete surprise,” he said.

The lucky discovery 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, Dr Tucker said.

“It’s a relic of a simpler time, when the universe was still slowing down and dark energy was not doing crazy stuff,” he said.

“We can use that to work out how dark matter and dark energy have messed up the universe.”

Paper:

http://science.sciencemag.org/content/347/6226/1123

Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens
BY PATRICK L. KELLY, STEVEN A. RODNEY, TOMMASO TREU, RYAN J. FOLEY, GABRIEL BRAMMER, KASPER B. SCHMIDT, ADI ZITRIN, ALESSANDRO SONNENFELD, LOUIS-GREGORY STROLGER, OR GRAUR, ALEXEI V. FILIPPENKO, SAURABH W. JHA, ADAM G. RIESS, MARUSA BRADAC, BENJAMIN J. WEINER, DANIEL SCOLNIC, MATTHEW A. MALKAN, ANJA VON DER LINDEN, MICHELE TRENTI, JENS HJORTH, RAPHAEL GAVAZZI, ADRIANO FONTANA, JULIAN C. MERTEN, CURTIS MCCULLY, TUCKER JONES, MARC POSTMAN, ALAN DRESSLER, BRANDON PATEL, S. BRADLEY CENKO, MELISSA L. GRAHAM, BRADLEY E. TUCKER
SCIENCE06 MAR 2015 : 1123-1126
Light from a distant supernova at z = 1.491 is detected in four images after being deflected en route by gravitational forces.

Abstract

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster’s gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.

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