International Liquid-Mirror Telescope (ILMT)

A new telescope facility has been launched in top of the Himalayan range that will keep a watch on the overhead sky.

• It can identify transient or variable objects such as supernovae, gravitational lenses, space debris, and asteroids.

Highlights of the event

• It is the first liquid mirror telescope in the country and the largest in Asia.
• The novel instrument employs a 4-meter-diameter rotating mirror made up of a thin film of liquid mercury to collect and focus light.
• It has been developed by the scientists of India, Belgium and Canada.
• It is located at an altitude of 2450 metres at the Devasthal Observatory campus of Aryabhatta Research Institute of Observational Sciences (ARIES).
  
  

What is liquid mirror telescope?

• Liquid-mirror telescopesare telescopes with mirrors made with a reflective liquid.
• The most common liquid used is mercury, but other liquids will work as well (for example, low-melting alloys of gallium).
• The liquid and its container are rotated at a constant speed around a vertical axis, which causes the surface of the liquid to assume a paraboloidal shape.
• This parabolic reflector can serve as the primary mirror of a reflecting telescope.
• The rotating liquid assumes the same surface shape regardless of the container's shape; to reduce the amount of liquid metal needed, and thus weight, a rotating mercury mirror uses a container that is as close to the necessary parabolic shape as possible.
• Liquid mirrors can be a low-cost alternative to conventional large telescopes.
• Compared to a solid glass mirror that must be cast, ground, and polished, a rotating liquid-metal mirror is much less expensive to manufacture.

How does it work?

• It has spun a pool of mercury which is a reflective liquid, so that the surface curved into 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.
• The rotation of the earth causes the images to drift across the camera, but this motion is compensated electronically by the camera itself.
• This mode of operation increases observing efficiency and makes the telescope particularly sensitive to faint and diffuse objects.

Significance

• ILMT is the first liquid-mirror telescope designed exclusively for astronomical observations.
• Devasthal Observatory now hosts two four-meter class telescopes – the ILMT and the Devasthal Optical Telescope (DOT).
• Both are the largest aperture telescopes available in the country.
• It is based on the application of Big Data and Artificial Intelligence/Machine Learning (AI/ML) algorithms that will be implemented for classifying the objects observed.
• The data collected from ILMT will be ideally suited to perform a deep photometric and astrometric variability survey over a period of typically 5 years.

Consequences

• Cost: The greatest advantage of a liquid mirror is its small cost, about 1% of a conventional telescope mirror. This cuts down the cost of the entire telescope at least 95%.
• Alignment problem: But the greatest disadvantage is that the mirror can only be pointed straight up.
• Research is underway to develop telescopes that can be tilted, but currently if a liquid mirror were to tilt out of the line and it can lose its shape.
• Health: Since mercury metal and its vapour are both toxic to humans and animals, there remains a problem for its use in any telescope where it may affect its users and others in its area.