Cosmic Hall of Mirrors Distorts Distant Galaxies

A new study reveals how bending of light from very distant galaxies, known as gravitational lensing, causes their images to be magnified and distorted, so there appear to be more than are actually there. Stuart Wyithe of the University of Melbourne’s School of Physics, explained the most distant galaxies were being viewed through a kind of cosmic hall of mirrors.

“There are only a few direct lines-of-sight to very distant objects in space. Our finding shows images from the earliest galaxies reach us more often via a gravitationally bent path. What you see is not exactly what is really there,“ he said.

“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, who is lead author on a paper published in the journal Nature on January 14, 2011, said a key goal of the Hubble Space Telescope over the past decade has been to look for the most distant galaxies and to help answer the questions of how and when the first generation of galaxies formed in the Universe.

However, the study, conducted together with colleagues from Ohio State University, Arizona State University and University of Manchester, makes the case that the Hubble Telescope’s existing view of the most distant galaxies is already significantly modified by gravitational lensing. Wyithe said future surveys will need to be designed to account for a significant gravitational lensing bias in high-redshift galaxies at these distances.

“Only the James Webb Space Telescope, if finished as designed, can ultimately make sense out of this gravitationally biased view of the distant universe, because it will have exquisite resolution and sensitivity at longer wavelengths to disentangle these very distant objects from the foreground lensing galaxies.”

Professor Wyithe said that Albert Einstein showed that gravity caused light to bend. The effect is normally extremely small, but when light passes close to a very massive object such as a galaxy, or a supermassive black hole, the bending of the light rays becomes more easily noticeable. 

“When light from a very distant galaxy passes a galaxy much closer to us, it can detour around the foreground galaxy, thus magnifying the light from the more distant galaxy directly behind it.

In previous studies, he said, gravitational lensing has been an interesting, but rare phenomenon.