Astronomers discover a cosmic 'mirage': A cluster of galaxies has created a unique 'lens' in outer space. Ruth McKernan reports

ITALIAN astronomers have found a rare cosmic 'mirage', a cluster of galaxies 5,000 million light years away whose combined gravity is acting like the lens of a huge galactic telescope, allowing the astronomers to see previously hidden distant stars.

Pictures revealing the gravitational lens were taken by the world's most advanced optical telescope, run by the European Southern Observatory on a remote mountain peak in the Chilean Andes. Yet the astronomers did not have to leave the comfort of their offices in Trieste.

By means of electronic datalinks, Massimo Ramella and Mario Nonino from the Astronomical Observatory aimed and focused the 3.5-metre New Technology Telescope 7,500 miles away at La Silla in Chile. Use of the system, called 'remote observing', can give astronomers complete control of the most sophisticated telescopes from anywhere in the world.

Only eight examples of gravitational lensing are known and this is the first to be found by remote observing.

The lens is formed by a cluster of galaxies known as EMSS 2137- 27, in the southern constellation of Capricornicus.

The light from the galaxies was emitted about 5,000 million years ago - the same time as our solar system was formed.

A gravitational lens is formed when a cluster has such a large mass (maybe more than 10 million million times the mass of our sun) that its gravity bends light from the matter behind it and focuses it, making it visible from Earth.

According to Dr Richard West, senior astronomer of the European Southern Observatory, gravitational lenses may help solve a long-standing puzzle about how much matter there is in the cosmos.

'Light, distorted by the lens, provides information from which we can calculate precisely how much matter is in the world around those galaxies and compare this with the amount we can see.

'If, for example, there is 10 times more than we can see, it means that the universe will not expand forever.

'If we can see everything, then it means that the universe is infinite,' he explained.

Dr Fred Watson from the Royal Observatory in Edinburgh said: 'Gravitational lenses have sprung to prominence in the last five years, although they were predicted by Einstein's theory of relativity 80 years ago.'

Dr Watson likened the gravitational lens to a galactic-sized telescope. 'A gravitational lens is almost like using a cluster of galaxies as a telescope to observe the younger galaxies, or quasars, which lie behind it.

'By examining the pattern of light we can refine our models of the nature of the universe we live in,' he said.

Although Britain is not a member of the European Southern Observatory, 'the UK has been at the forefront of the development of remote observing', said Ian Robson, Professor of Astronomy at the University of Lancashire.

British astronomers are now moving on to the next stage - 'remote eavesdropping' - where the scientist gives instructions, by computer, to highly trained operators at the telescope's location, rather than having sole control of the telescope themselves.

This is more cost effective and has the advantage of flexible scheduling, Professor Robson said. Experiments can be performed which optimise the prevailing weather conditions and make more efficient use of the telescope.

The British, Americans and Canadians are jointly planning to build two eight-metre telescopes, more than twice the size of the one at La Silla used by the Italians.

The twin telescopes, the 'Gemini project', are to be built in Hawaii and Chile, considered to be the best locations for astronomical observation.

In addition, the European Southern Observatory intends building four eight-metre telescopes, linked together, at its Chilean observatory.