Astronomers take vision to the limit

By Dr David Whitehouse
BBC News Online science editor

Astronomers from the European Southern Observatory (Eso) organisation have successfully tested a device that corrects for the distortions introduced into an astronomical image by the turbulence of the Earth's atmosphere.

A sharp view of the galactic centre

Although not the first device of its type, experts say that the MACAO-VLTI (Multi Application Curvature Adaptive Optics - Very Large Telescope Interferometer) instrument is a frontrunner in making ground-based telescopes as good as those in space.

The first observations, made on 18 April, have been released showing how the device can compensate for the blurring atmosphere, producing sharp images of nearby double stars as well as the centre of our galaxy.

The next step is to make more of them and place them on a series of telescopes so that signals from them all can be combined, synthesising the view that would be obtained from an unbuildable super telescope.

Limits of detectability

The instrument works by applying minute corrections to the mirror receiving light from the stars. These corrections are based on an analysis of the distorted light from the star and are made in real-time.

The first object seen with the new device was a nearby double star.

Called HIC 59206, it is difficult to see the two component stars using traditional ground-based telescopes.

HIC 59206 before...

However, MACAO-VLTI has no problems in splitting them.

Another region observed was the mysterious centre of our galaxy.

Located about 30,000 light-years away behind the obscuring dust clouds of Sagittarius, the centre of our galaxy is a confusing collection of bright and faint sources, many of which hover around the limits of detectability.

MACAO-VLTI produces a clear picture of this complicated but important region inside which there may be a supermassive black hole at our galaxy's heart.

After testing, it is hoped the device will be able to penetrate close to the central black hole.

Greater precision

Eventually, the adaptive optics device will be connected to several of the 8.2-metre telescopes at the Paranal Observatory - the four units that comprise the Very Large Telescope (VLT) facility.

Light beams from the VLT telescopes, after they have been corrected for atmospheric turbulence, will be brought together and combined.

...and after

After much computer processing, an image will be produced similar to that which would be obtained using a larger telescope than the individual ones.

It is a technique that has been used in radio astronomy for decades. Introducing it into optical astronomy has taken a long time because of the much smaller wavelengths in the visible part of the spectrum compared with the radio region.

This makes the tolerances and precision required to combine the light beams much tighter and it is only in recent years that it has been practicable.