ULiège at the origin of a unique liquid mirror telescope in the Indian Himalayas

"First light" for the International Liquid Mirror Telescope (ILMT) on the Devasthal Peak site. A project led by Prof. Jean Surdej and developed with the CSL and AMOS.

Astronomers in India, Belgium and Canada have a new tool with which to view the cosmos with the commissioning of the International Liquid Mirror Telescope (ILMT). Located at Devasthal Peak (2450 metres altitude) in the central Himalayan range in India, this novel instrument employs a 4-metre-diameter rotating mirror, covered with a thin film of liquid mercury, to collect and focus light. The telescope is designed to survey the strip of sky passing overhead each night, allowing it to identify transient or variable objects such as supernovae, gravitational lenses, space debris, asteroids, etc.

“The collected data will be ideally suited to perform a deep photometric and astrometric variability survey over a period of typically 5 years” notes Project Director Prof.  Jean Surdej (University of Liège and University of Poznan, Poland).

Liquid-mirror telescopes take advantage of the fact that the surface of a rotating liquid naturally takes on a parabolic shape, which is ideal for focusing light. A thin transparent film of mylar protects the mercury from wind. The reflected light passes through a sophisticated multi-lens optical corrector that produces sharp images over a wide field of view. A large-format electronic camera, located at the focus, records the images. Prof. Paul Hickson (University of British Columbia, Canada), an expert on liquid mirror technology, added that “the rotation of the earth causes the images to drift across the camera, but this motion is compensated electronically by the camera. This mode of operation increases observing efficiency and makes the telescope particularly sensitive to faint and diffuse objects.”

“ILMT is the first liquid-mirror telescope designed exclusively for astronomical observations installed at the Devasthal site of ARIES” mentioned ARIES Director Prof. Dipankar Banerjee. Prof. Banerjee mentioned that Devasthal site now hosts two four-metre class telescopes – the ILMT and the Devasthal Optical Telescope (DOT). Both are the largest aperture telescopes available in the country.

“When regular science operations begin later this year, the ILMT will produce about 10 GB of data every night, which will be quickly analyzed to reveal variable and transient stellar sources” said Dr. Brajesh Kumar, ILMT Project Scientist. The 3.6 meter DOT, with the availability of sophisticated back-end instruments, will allow rapid follow-up observations of the newly-detected transient sources with the ILMT.

“The wealth of data generated with the ILMT survey will be exemplary. In future, several young researchers will be working on different science programs utilizing the ILMT data" said Dr. Kuntal Misra who is the Project In-charge of ILMT at ARIES. Prof. Banerjee is enthusiastic about the application of Big Data and Artificial Intelligence/Machine Learning (AI/ML) algorithms that will be implemented for classifying the objects observed with the ILMT. He stated, “I am hopeful that this project will attract and motivate several young minds from scientific and engineering backgrounds to take up challenging problems.”

The ILMT collaboration includes researchers at the Aryabhatta Research Institute of observational sciencES (ARIES, an autonomous institute under the Department of Science and Technology (DST), Govt. of India) and the Indian Space Research Organization (ISRO) in India, the University of Liège and the Royal Observatory of Belgium in Belgium, Poznan Observatory in Poland, the Ulugh Beg Astronomical Institute of the Uzbek Academy of Sciences and National University of Uzbekistan, the University of British Columbia, Laval University, the University of Montreal, the University of Toronto, York University and the University of Victoria in Canada.

The telescope was designed and built by the AMOS corporation and the Centre Spatial de Liège in Belgium.

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International Liquid Mirror Telescope (ILMT)

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Pr Jean Surdej