Young Galaxies Disorting Our View of the Ancient Universe

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Nearby bright galaxies have been distorting the view of the earliest galaxies, which are important in understanding what happened to the universe just after the Big Bang, researchers report, requiring future studies of the universe's earliest galaxies will need to be corrected for the bias.

The first gravitational lens, a phenomenon in which light from a distant object is bent around a massive foreground object, was discovered in 1979 by a team led by Dr. Dennis Walsh from The University of Manchester’s Jodrell Bank Observatory.


Since then, astronomers have used gravitational lenses in many ways, including studying dark matter and as “Nature’s Telescope” to investigate galaxies in the distant universe.

In a letter to the journal Nature, Professor Shude Mao of The University of Manchester, along with Stuart Wyithe (University of Melbourne), Haojing Yan (Ohio State University) and Rogier Windhorst (Arizona State University), have calculated that gravitational lenses allow us to see farther into space than previously thought.

They argue that gravitational lensing makes faint sources more visible and this effect may be even more important than originally thought when looking at distant galaxies.

Acting like a cosmic magnifying glass, gravitational lensing brings into clearer view galaxies which would otherwise be beyond the reach of even the largest telescopes.

Professor Mao said: “The magnifying effect of gravitational lensing gives us a much better chance of seeing very distant objects in the universe, otherwise too faint to see, and study them in far greater detail.”

In their Nature letter, Professor Mao and his colleagues suggest that our measurement of the brightnesses and numbers of very distant galaxies is likely to be significantly distorted by the magnification caused by individual foreground galaxies much closer to us.

But the exact ratio of numbers of magnified and unmagnified distant galaxies depends on various factors which astronomers are currently not certain about.

Professor Mao added: “Next-generation telescopes such as the James Webb Space Telescope, due to be launched in 2014, will be able to determine this effect more precisely.

“By studying these extremely distant objects we can see far back in time. We aim to exploit the magnifying effect of gravitational lensing to reveal how galaxies like our own Milky Way emerged from the early Universe.”

The study, published in the journal Nature, revealed that the phenomenon is likely to occur in at least 30% of observations of the early galaxies. "What this shows is that gravitational lensing will lead to a higher number of distant galaxies being counted in future surveys, at times when the universe was less than 500 million years old," Wyithe said.

Using images from the Hubble Space Telescope, the team measured the separation between older, more distant galaxies and brighter and younger foreground galaxies. They compared what they saw to a mathematical model that takes in account gravitational lensing, and concluded that the ancient galaxies were seen to be larger, brighter and more distorted than they actually are.

This effect has likely resulted in inaccurate counts for number density of ancient galaxies as seen by the recent near-IR surveys with the Hubble Space Telescope Wide Field Camera 3, according to the researchers.

But, in a twist, this effect may help astronomers find these distant, hard-to-see galaxies. "The lensing acts as a natural telescope too, so it can also help us find these distant galaxies,” said Wyithe.

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