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Tom Feilden | 18:00 UK time, Thursday, 4 November 2010

Two galaxies show the effect of gravitational lensing

Any child can tell you that light travels in straight lines, but it takes a genius like Albert Einstein to appreciate that (with apologies to George and Ira Gershwin) it ain't necessarily so.

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."

How gravitational lensing works

How gravitational lensing works

The magnification created by the effect of gravitational lensing allows astronomers to see galaxies that would otherwise be hidden, providing key insights into the history of the cosmos and bringing us a step closer to understanding the complex birth of stars and galaxies.

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."


  • Comment number 1.

    I once read an scientific article that said the human eye cannot detect all there is to be seen; it is very limited I think the percentage of the spectrum was something like 40%.). So too for hearing, touch, and all the other senses. We are not sufficiently evolved to truly "see" what exists around us - like flowers or trees or grass...or even one another.
    I know that light is made up of packets of energy, called photons. This makes it seem like light travels in a straight line, but in fact photons can be disrupted. Whatever the source of light, if the medium is non-intrusive, light will appear to traavel in a straight line.
    When light rays move from one medium to another, such as from air to water, linear paths are altered. Light, in a vacuum moves at more than 186,000 miles per second, or 300,000 kilometers per second; so, you cannot see individual particles, photons, which may be waves or particules.
    What I'm saying is magnification, gravitational lensing, etc. does not really allow astronomers to see galaxies that would otherwise be hidden:
    1. because our human vision is so very limited and
    2. the light takes a long, long, LONG time to reach us
    3. so the universal object may no lonbger be there.
    We may be children of the universe, but we are fairly blind children of the universe.

  • Comment number 2.

    I very much enjoyed reading this blog entry. I might not have Einstein's maths, but I've got the idea!


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