"Nature's telescopes" help us see distant galaxies

As powerful as our modern telescopes are, it is still extraordinarily difficult for us to observe very distant galaxies.  Luckily, nature sometimes lends us a hand through a process called gravitational lensing

Albert Einstein first predicted in his general theory of relativity that light from a distant object could be bent by the gravity of an object sitting in front of it; if two objects were aligned just right, the light from the distant object would form a perfect ring around the closer object.  Astronomer Fritz Zwicky later predicted that massive galaxy clusters would be able to bend the light from galaxies positioned behind them.  Indeed, we've observed galaxies and galaxy clusters with distinctive arcs surrounding them - these arcs are the light from background objects that have been "lensed."

The large red galaxy in this image is acting as a gravitational lens.  Light from a more distant blue galaxy is being lensed by the red galaxy's gravity and bent into the blue arcs seen here (Image credit: ESA/Hubble; NASA). 

The large red galaxy in this image is acting as a gravitational lens.  Light from a more distant blue galaxy is being lensed by the red galaxy's gravity and bent into the blue arcs seen here (Image credit: ESA/Hubble; NASA). 

The light from lensed objects isn't just bent - it is also magnified.   This enables us to detect objects much fainter and more distant than we would normally be able to see.  There is still much to learn about the first galaxies: how fast they were forming stars, if they had active black holes, and how they evolved into the galaxies we see today.  Gravitational lensing gives us a way to study these galaxies until our telescopes are able to observe them.  

The Hubble Space Telescope is currently carrying out a project known as Frontier Fields.  Over the course of three years, Hubble will take deep observations of six galaxy clusters that are lensing and magnifying the light from distant galaxies behind them.   We've already begun to learn about distant galaxies from these observations; one of the first discoveries to come out of the Frontier Fields project was that of one of the most distant galaxies ever observed!  Thanks to the gravitational lensing done by galaxy cluster Abell 2744, astronomers were able to study a galaxy over 13 billion light years away.  Observed as it was just 650 million years after the Big Bang, Abell 2744_Y1 is 30 times smaller than the Milky Way but forming ten times as many stars!

When the James Webb Space Telescope launches in 2018, we'll be able to study some of these early galaxies more easily.  Until then, we've got help from nature's telescopes.

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