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World’s largest liquid mirror telescope goes online

Ask any astronomer, astrophysicist or cosmologist, and they will probably tell you that a new age of astronomy is upon us. Between the advances in gravitational-wave astronomy, the explosion in exoplanet studies, and the next generation of ground-based and space-based telescopes coming online, it’s pretty apparent that we’re on the verge of an age of near-continuous discovery. As always, top discoveries, innovations, and the things they enable inspire scientists and researchers to look to the future and take the next big step.

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

Like other observatories, the ILMT is located high 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 Uttarakhand province in northern India (western Nepal). ). The telescope is designed to survey the sky and identify objects such as supernovae, gravitational lensing, space debris, asteroids, and other transient and variable phenomena.

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

Dr. Paul Hickson, a UBC professor of physics and astronomy and a pioneer of liquid mirror technology, has been perfecting the technology over the years at the Large Zenith Telescope (LZT). Located at 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 his expertise, Dr. Hickson and his colleagues played a critical role in the design and creation of the ILMT air system. The facility received its first light last May and will temporarily go out of operation in October due to India’s monsoon season.

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 dish that contains a reflective liquid (such as mercury), a rotating section on which the liquid mirror (LM) sits (powered by air compressors), and a drive system. When turned 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 small ripples (due to wind or rotation) from forming.

Liquid mercury offers a low-cost 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 at the focus records the images. As Dr. Hockson explained in a UBC Science press release:

“By 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 causes the images to move around the camera, but this movement is compensated for electronically.

“The camera has a corrective lens that was specially designed to remove the curvature of the Star Trail. The stars go in circles around the north celestial pole, around the Pole Star. If you take a time exposure, the stars don’t go in a straight line, they go in arcs or circles. But this corrector is designed to correct for that and remove the curvature to straighten out the Star Trails, giving us sharp images.”

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

Regular science operations are scheduled to begin later this year. At this point, the ILMT is expected to collect around 10GB 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-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 the ILMT and the ancient Devesthal Temple, the DOT has the distinction of being the largest optical telescope in India.

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

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

Other readings: UBC

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