To better understand the early universe, adaptive optics technique invented

Jan 17, 2011
Images recorded in the near infrared (1.65 microns) by CANARY: left, without any correction, right, with MOAO correction recovering the telescope's diffraction limit. Credit: Equipe CANARY

Adaptive optics makes it possible to remove distortions caused by turbulence in the atmosphere when observing the sky. A major innovation in this field has been achieved by a Franco-British team, including astronomers from the Paris Observatory, CNRS and Universite Paris Diderot. This new technique has for the first time been tested and validated under real conditions using the CANARY prototype mounted on a telescope in La Palma (Spain). It enables scientists to observe very faint astronomical sources over a much wider field of view than was previously possible. In the future, this innovative system may be included in one of the instruments that will equip ESO's European Extremely Large Telescope in Chile. It will make it possible to study the early Universe and better understand its evolution.

Observation of the first stars and galaxies that formed in the , 800 million years after the , requires a really large telescope. ESO's European Extremely Large Telescope (E-ELT) will have a mirror 42 meters in diameter and will be built at an altitude of 3060 meters in the Atacama Desert in Chile. However, like all its ground-based counterparts, it will inevitably undergo the effects of , which blurs images and reduces their contrast and resolution. To correct such distortions, it will need to be equipped with a technology known as adaptive optics. This works by using a deformable mirror that compensates in real time the early or late arrival of wavefronts of light after they propagate through the atmosphere. But this could only work over a very narrow field of view until now. However, in order to survey the early Universe in detail, need fields of view that are at least ten times wider.

The William Herschel telescope at Roque de Los Muchachos, La Palma (Canary Islands), and laser shot. Credit: Tibor Agocs (ING)

To achieve such performances, the EAGLE multi-object imaging , which should equip the E-ELT, is being developed in France and the UK. Its goal is to make it possible to simultaneously observe 20 distant galaxies within 5 arcminutes (1/6 of the diameter of the full Moon), each one of which will be corrected for atmospheric distortion. However, these primordial galaxies, present in the very first moments of the Universe, are too faint to allow any direct measurement of . Such measurement therefore has to be based on information from the light of the few guide stars present in the field of view, along with the generation of artificial laser guide stars when natural guide stars are insufficient. Under these conditions, compensating turbulence with a single deformable mirror is no longer as efficient as in conventional adaptive optics. Since primordial galaxies have a very small apparent size (approximately one arcsecond), it is only necessary to correct small parts of the images that correspond to the galaxies being observed. It was on this basis that the researchers developed a novel adaptive optics technology called Multi-Object Adaptive Optics (MOAO). This innovative system uses one deformable mirror per target galaxy (20 in all). For each one of them, the mirror is deformed on the basis of measurements taken on all guide stars in the field of view, by means of a tomographic survey of the atmosphere.

Installed on the CANARY prototype, this new technique has for the first time been validated under real on-sky conditions at the 4.2 meter diameter William Herschel telescope in La Palma, Canary Islands, Spain. The measurements were carried out on three guide stars located at a considerable distance from the test star for which the correction of image degradation was modelled. This compensation was applied 150 times per second to the deformable mirror placed in the light beam from the test star. CANARY's performance lived up to expectations: the quality of the image obtained was very close to that measured using a conventional adaptive optics method under similar conditions. Astronomers now benefit from an technique that will enable them to survey a field of view over 10 times larger than those available until now. The next step will be to repeat this experiment with the same prototype, using artificial laser-generated guide stars. If the technology meets expectations, it will equip ESO's E-ELT.

Explore further: Comet Jacques makes a 'questionable' appearance

add to favorites email to friend print save as pdf

Related Stories

Taking the twinkle out of the night sky

Aug 04, 2010

If you are like most people, you probably enjoy the twinkling of stars that blanket the sky on a clear summer night. If you are an astronomer, chances are you find it extremely annoying.

New Adaptive Optics technique demonstrated

Mar 30, 2007

On the evening of 25 March 2007, the Multi-Conjugate Adaptive Optics Demonstrator (MAD) achieved First Light at the Visitor Focus of Melipal, the third Unit Telescope of the Very Large Telescope (VLT). MAD allowed the scientists ...

Free from the Atmosphere

Jun 13, 2007

An artificial, laser-fed star now shines regularly over the sky of Paranal, home of ESO's Very Large Telescope, one of the world's most advanced large ground-based telescopes. This system provides assistance ...

The Rise of a Giant

Dec 11, 2006

European astronomy has received a tremendous boost with the decision from ESO's governing body to proceed with detailed studies for the European Extremely Large Telescope. This study, with a budget of 57 million ...

The Planet, the Galaxy and the Laser

Aug 03, 2007

On the night of 21 July, ESO astronomer Yuri Beletsky took images of the night sky above Paranal, the 2600m high mountain in the Chilean Atacama Desert home to ESO's Very Large Telescope. The amazing images ...

SINFONI Opens With Upbeat Chords

Aug 24, 2004

ESO's Very Large Telescope welcomes the first ever adaptive optics assisted spectrograph on an 8-m class telescope: SINFONI. During the successful commissioning of the Adaptive Optics Module, exceptional ima ...

Recommended for you

Comet Jacques makes a 'questionable' appearance

12 minutes ago

What an awesome photo! Italian amateur astronomer Rolando Ligustri nailed it earlier today using a remote telescope in New Mexico and wide-field 4-inch (106 mm) refractor. Currently the brightest comet in ...

Image: Our flocculent neighbour, the spiral galaxy M33

21 minutes ago

The spiral galaxy M33, also known as the Triangulum Galaxy, is one of our closest cosmic neighbours, just three million light-years away. Home to some forty billion stars, it is the third largest in the ...

Image: Chandra's view of the Tycho Supernova remnant

Jul 25, 2014

More than four centuries after Danish astronomer Tycho Brahe first observed the supernova that bears his name, the supernova remnant it created is now a bright source of X-rays. The supersonic expansion of ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (1) Jan 17, 2011
Question born of laziness:

Do they compare observations from land based adaptive optics to space borne observations?