TWO GALAXIES FOR THE PRICE OF ONE
Einstein's theory of General Relativity showed that gravity can bend light - a phenomenon known as gravitational lensing, and one which was spectacularly confirmed by a team lead by Sir Arthur Eddington in 1919.
The effect is normally extremely small, and it is only when light passes close to a very massive object, such as a galaxy containing hundreds of billions of stars, that it can be spotted.
Take a close look at the two images above. The first, taken by ESA's Herschel Space Observatory, shows an unusually bright orange blob located in the constellation Hydra.
The second, taken at higher resolution from the ground-based Keck Telescope and the Smithsonian Astrophysical Observatory's Submilimetre Array in Hawaii, shows that Herschel has found a gravitational lens.
The reason why this blob is so bright is that we are actually seeing two galaxies, with the red light from the more distant one bent around and superimposed over the light emanating from the nearer, blue, galaxy.
If light really did travel in straight lines we might expect the much longer wavelength light from the background galaxy to be "blotted out" by the stronger signal from the closer one. Instead this longer wavelength light has been magnified and distorted by gravitational lensing.
The overall effect is to increase the brightness, making the orange blob appear considerably closer to earth than it really is.
The images, published in the journal Science, are the first to come from the Herschel-ATLAS project - the largest imaging survey at sub-milimetre wavelengths conducted so far with ESA's Herschel Observatory.
The lead author, Dr Mattia Negrello from the Open University, says the findings will help to pinpoint many more examples of this rare phenomena.
"The big breakthrough is that we have discovered many of the brightest sources are being magnified by lenses," he explains.
"Which means we no longer have to rely on the rather inefficient methods at visible and radio wavelengths to find them."
According to Professor Rob Ivison from the Royal Observatory, Edinburgh, the technique promises to unlock the secrets of how galaxies form and evolve.
"Not only does the lensing allow us to find them very efficiently, but it helps us to peer within them to figure out how the individual pieces of the jigsaw came together back in the mists of time."