The world’s largest liquid mirror telescope comes online

Ask any astronomer, astrophysicist, or cosmologist, and they’ll probably tell you that a new era of astronomy is dawning! Between breakthroughs in gravitational wave astronomy, the explosion in exoplanet studies, and the new generation of ground and space telescopes coming online, it’s pretty clear that we’re on the cusp of an era of nearly continuous discovery! As always, great discoveries, innovations and the things they make possible 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 collection to advance the science of astronomy. A groundbreaking example is the newly commissioned International Liquid Reflecting Telescope (ILMT) telescope that just came online on Devasthal Peak, a 2,450 m (8,040 ft) high mountain in the central Himalayas. Unlike conventional telescopes, the ILMT relies on a rapidly rotating 4-meter (13 ft) mirror coated with a layer of mercury to collect cosmic light.

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

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

dr. Paul Hicksona UBC Physics and Astronomy Professor and pioneer of liquid mirror technology, has perfected the technology over the years on the Large Zenith Telescope (LZT). Located in UBC’s Malcolm Knapp Research Forest east of Vancouver, BC, the LZT was the largest liquid metal mirror before the ILMT was commissioned. Because of their expertise, Dr. Hickson and his colleagues played a critical role in designing and creating the ILMT air system. The facility received its first light last May and will be temporarily shut down in October due to the monsoon season in India.

While it may sound like something out of science fiction, the basics of this technology are quite simple. The technology boils down to three components, including a shell containing a reflective liquid (such as mercury), a rotating section that holds the Liquid Mirror (LM) (powered by air compressors), and a drive system. When switched on, the LM takes advantage of the fact that the rotational force causes the mirror to assume a parabolic shape, which is ideal for focusing light. Meanwhile, the liquid mercury is protected by an extremely thin layer of optical-grade mylar that prevents the formation of small waves (by wind or the rotation).

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

“The mirror rotates once every eight seconds and floats on a film of compressed air about 10 microns thick. By comparison, a human hair is about 70 microns thick. The 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 causes the images to float over the camera, but this movement is electronically compensated.

“The camera has a corrector lens specially designed to remove the curvature of star trails. Stars revolve in circles around the northern celestial pole, around the North Star. When you take a time exposure, the stars don’t go in straight lines, but in arcs or circles. But this corrector is designed to correct for that by removing the curvature to straighten out the star trails, giving us sharp images.”

The 3.6 m Devasthal optical telescope at night. Credit: ARIES

Regular scientific operations will start later this year. At this point, the ILMT is expected to collect about 10 GB of data each night that will be analyzed for stellar sources. These sources will then be selected for follow-up observations using the 3.6 meters (11.8 ft) Devasthal optical telescope (DOT) and its advanced spectroscopic instruments. As part of a facility overseen by the Aryabhatta Research Institute of Observational Sciences (ARIES) – which includes the ILMT and the ancient Devesthal Temple – the DOT stands out as the largest optical telescope in India.

In particular, the ILMT will look for 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 that hinder them (planets, dust rings, etc.). Transient phenomena, on the other hand, refer to short-lived events such as supernovae, Fast-Radio Burts (FRBs), gamma-ray bursts (GRBs), gravitational microlensing, etc. The study of these objects will lead to breakthroughs in astrophysics and cosmology.

In addition to ARIES and UBC, other organizations that are part of the ILMT collaboration are the Indian Space Research Organization (ISRO), the Ulugh Beg Astronomical Institute (portion of the Uzbek Academy of Sciences), the University of Liège, the Royal Observatory of BelgiumPoznan Observatory in Poland, Laval University, University of Montreal, University of Toronto, York University and University of Victoria in Canada.

Read further: UBC

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