The world’s largest liquid mirror telescope is online

Ask any astronomer, astrophysicist or cosmologist, and they’ll probably tell you that a new era of astronomy is upon us! Between breakthroughs in gravitational wave astronomy, the explosion of exoplanet studies, and the coming online of next-generation ground-based and space-based telescopes, it’s pretty clear that we’re on the eve of an age of near discovery. keep on going ! As always, breakthrough discoveries, innovations, and the things they enable inspire scientists and researchers to look ahead and take the next big step.

Take, for example, research into liquid mirrors and advanced interferometers, which would rely on entirely new types of telescopes and light-gathering to advance the science of astronomy. A pioneering example is the recently commissioned International Liquid Mirror Telescope (ILMT) which has just come online at Devasthal Peak, a 2,450 m (8,040 ft) high mountain in the central Himalayan range. Unlike conventional telescopes, the ILMT relies on a rapidly rotating 4-meter (13-foot) mirror coated in a layer of mercury to capture cosmic light.

Like other observatories, ILMT is located above sea level to minimize distortion caused by atmospheric water vapor (a phenomenon known as atmospheric refraction). Like ESO’s Paranal Observatory in northern Chile or the Mauna Kea Observatories in Hawaii, the ILMT telescope is part of the Devasthal Observatory located in the remote mountains of the province of Uttarakhand in northern India (west of Nepal). The telescope is designed to probe the sky and identify objects such as supernovae, gravitational lenses, space debris, asteroids, and other transient and variable phenomena.

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An image of the ILMT mirror taken during testing in Liège, Belgium. Credit: Collaboration ILMT/University of Liège

Dr. Paul Hickson, professor of physics and astronomy at UBC and a pioneer in liquid mirror technology, has perfected the technology over the years at the Large Zenith Telescope (LZT). Located in UBC’s Malcolm Knapp Research Forest, east of Vancouver, British Columbia, the LZT was the largest liquid metal mirror before ILMT was commissioned. Because of their expertise, Dr. Hickson and his colleagues played a central role in the design and creation of the ILMT Air System. The installation gathered its first light last May and will temporarily cease operations in October due to India’s monsoon season.

Although it may sound like science fiction, the basics of this technology are quite simple. The technology comes down to three components, including a dish containing a reflective liquid (like mercury), a rotating section on which the liquid mirror (LM) sits (powered by air compressors), and a drive system. When energized, the LM takes advantage of the rotational force causing the mirror to take on a parabolic shape, which is ideal for focusing light. Meanwhile, the liquid mercury is protected by an extremely thin layer of optical grade mylar which prevents the formation of small waves (due to wind or rotation).

Liquid mercury offers an inexpensive alternative to glass mirrors, which are very heavy and expensive to produce. The reflected light passes through a sophisticated multi-lens optical corrector while a large format electronic camera in focus records the images. As Dr. Hockson explained in a UBC Science press release:

“Rotating once every eight seconds, the mirror floats on a film of compressed air about 10 microns thick. For comparison, a human hair is about 70 microns thick. Air bearings are so sensitive that even smoke particles can damage them. A second air cushion prevents the rotor from moving sideways. The rotation of the Earth drifts the images through the camera, but this movement is electronically compensated.

“The camera is equipped with a corrector lens specially designed to remove the curvature of star trails. The stars circle around the north celestial pole, around the pole star. If you take a time exposure, the stars don’t go in straight lines, they go in arcs or circles. But this corrector is designed to fix that to remove the curvature to straighten out star trails, giving us sharp images.

The Devasthal 3.6m Optical Telescope at night. 1 credit

Regular science operations are expected to begin later this year. At this point, ILMT should collect around 10 GB of data each night which will be analyzed for stellar sources. These sources will then be selected for follow-up observations using the 3.6-meter (11.8-foot) Devasthal Optical Telescope (DOT) and its sophisticated spectroscopic instruments. As part of a facility overseen by the Aryabhatta Research Institute of Observational Sciences (ARIES) – which includes ILMT and the ancient Devesthal Temple – the DOT has the distinction of being the largest optical telescope in India.

In particular, ILMT will research astronomical phenomena that are at the forefront of astronomical research today. This includes variable objects, stars that vary in brightness over time due to changes in their physical properties, or objects obstructing them (planets, dust rings, etc.). Transients, on the other hand, refer to short-lived events such as supernovae, Fast-Radio Burts (FRBs), gamma-ray bursts (GRBs), gravitational microlenses, etc. The study of these objects will lead to breakthroughs in the fields of astrophysics and cosmology.

Apart from ARIES and UBC, other organizations that make up the ILMT collaboration include the Indian Space Research Organization (ISRO), Ulugh Beg Astronomical Institute (part of the Uzbek Academy of Sciences), the University of Liège, the Royal Observatory of Belgium, the Observatory of Poznan in Poland, Laval University, the University of Montreal, the University of Toronto, York University and the University of Victoria in Canada.

Further reading: UBC

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