India revives liquid mirror telescope technology

In partnership with the University of Liège, ARIES

an Indian research center dedicated to astronomy, has just commissioned the International Liquid Mirror Telescope (ILMT) at its Devasthal site in the Himalayas.
The mirror of 4 meters in diameter of this telescope is in fact a bowl of mercury put in rotation. The combination of gravity and centrifugal force pushes the liquid into a perfect parabolic shape, just like a conventional telescope mirror. This relative simplicity makes it possible to considerably reduce the price of the telescope by avoiding the operations necessary to produce the mirror of a traditional telescope: molding of the glass, preparation of the surface to receive a reflective aluminum film, etc.

By way of comparison, the IMLT manufactured by a Belgian, Canadian and Indian consortium cost 2 million dollars, while the optical telescope, equipped with a glass mirror 3.6 meters in diameter, built on the same site by the same consortium cost $18 million.

ARIES : Devasthal site in the Himalayas, at an altitude of 2500 meters The optical telescope nevertheless has some specific advantages such as allowing orientation and therefore a wider choice of target. Nevertheless, for Jean Surdej, professor at the University of Liège and director of the project, “simple things are often the best“. For many astronomers, liquid mirror technology would even be perfect on the Moon, with no atmosphere and no seismic activity. A team from the University of Texas at Austin is already proposing the construction of a telescope equipped with a liquid mirror 100 meters in diameter. This giant telescope, dubbed the Ultimately Large Telescope, could constantly focus on the same piece of sky for years from one of the Moon’s poles and collect the faint trickle of photons from the very first stars that lit up the universe. before galaxies even existed. The processing of the accumulated luminous flux would thus make it possible to study the most distant and oldest areas of the Universe. James Roger Prior Angel, professor of astronomy and optical sciences at the University of Arizona, believes that there is “an opportunity to build a large liquid mirror telescope that goes beyond what conventional telescopes can do“. Moreover, according to Ermanno Borra, a Canadian researcher from Laval University in Quebec, “

ionic liquids

(salts with low freezing points) could be adapted to lunar conditions and could replace mercury if made reflective with a thin layer of silver.

The liquid mirror telescope is not really new. The idea developed by the Laval University of Quebec, the University of British Columbia (UBC) and NASA since 1982, had allowed the realization of some telescopes beyond the prototype stage. However, the research had to be abandoned for budgetary reasons in the early 2000s.

With renewed interest in the Moon and the resumption of ambitious programs by most space agencies, the success of Devasthal’s ILMT could therefore revive a technology that has been neglected until now.
ARIES (Aryabhatta Research Institute of Observational Sciences)

The 3 meter liquid mirror telescope, used by NASA from 1996 to 2000as part of its space debris tracking program.Source: NASA

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