Key to the secrets of the Universe

December 3rd, 2010

Astronomers have discovered a new way of locating a natural phenomenon that acts like a zoom lens and allows a view at galaxies in the distant and early universe.

These results are from the first data taken as part of the Herschel-ATLAS project, the largest imaging survey conducted so far with the European Space Agency’s Herschel Space Observatory.

The magnification provides key insights into how galaxies have changed over the history of the cosmos.

Dr Loretta Dunne, from the School of Physics and Astronomy at The University of Nottingham, is jointleader of the Herschel-ATLAS survey.

She said: “What we’ve seen so far is just the tip of the iceberg. Wide area surveys are essential for finding these rare events and since Herschel has only covered one 30th of the entire Herschel-ATLAS area so far, we expect to discover hundreds of lenses once we have all the data. Once found, we can probe the early universe on the same physical scales as we can in galaxies next door.”

Gravity can cause light to bend. The effect is extremely small, and it is only when light passes close to a massive object such as a galaxy containing hundreds of billions of stars that the results become noticeable. When light from a very distant object passes a galaxy much closer to us, its path can be bent in such a way that the image of the distant galaxy is magnified and distorted.

These alignments are called “gravitational lenses” and many have been discovered, mainly at visible and radio wavelengths. The alignment is crucial, requiring precise position of the lens — in this case a galaxy. This is very rare. Astronomers have to rely on chance alignments, which often involves sifting through large amounts of data.

Most methods of searching for gravitational lenses have a very poor success rate. Herschel looks at far-infrared light, which is emitted by the gas and dust from which stars form. Its panoramic imaging cameras have allowed astronomers to find these lenses by scanning the sky in far-infrared and sub-millimetre light.

Lead researcher Dr Mattia Negrello, of the Open University, said: “The big breakthrough is that we have discovered that many of the brightest sources are being magnified by lenses, which means we no longer have to rely on the rather inefficient methods of finding lenses which are used at visible and radio wavelengths.”

The Herschel-ATLAS images contain thousands of galaxies, most so far away that the light has taken billions of years to reach us. Dr Negrello’s team used optical telescopes on Earth for look at the positions of five bright objects. They found galaxies that would not normally be bright at the far-infrared wavelengths observed by Herschel.

They suspected that these galaxies might be gravitational lenses magnifying much more distant galaxies seen by Herschel. To find the true distances to the Herschel sources, the team looked for a tell-tale signature of molecular gas. Using radio and sub-millimetre telescopes on the ground, they showed that this signature implies the galaxies are being seen as they were when the Universe was 2–4 billion years old — less than a third of its current age.

The galaxies seen by the optical telescopes are much closer, each ideally positioned to create a gravitational lens. Dr Negrello said that “previous searches for magnified galaxies have targeted clusters of galaxies where the huge mass of the cluster makes the gravitational lensing effect unavoidable. Our results show that gravitational lensing is at work in not just a few, but in all of the distant and bright galaxies seen by Herschel.”

Prof Rob Ivison, of the Royal Observatory, Edinburgh, part of the team that created the images, said: “This relatively simple technique promises to unlock the secrets of how galaxies like our Milky Way formed and evolved. Not only does the lensing allow us to find them very efficiently, but it helps us peer within them to figure out how the individual pieces of the jigsaw came together, back in the mists of time”.

Prof Steve Eales, from Cardiff University, and the other leader of the survey, added: “Eighty per cent of the matter in the Universe is thought to be dark matter, which does not absorb, reflect or emit light and so can’t be seen directly with our telescopes. With the large number of gravitational lenses that we’ll get from our full survey, we’ll really be able to get to grips with this hidden Universe.” Visit: http://www.h-atlas.org.

Photo courtesy of Herschel-ATLAS.

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