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India’s scientists make low-cost optical telescope for seeing distant quasars, galaxies

A collage showing pictures of the 3.6-m Devasthal Optical Telescope (DOT), the ‘Made-in-India’ ARIES-Devasthal Faint Object Spectrograph and Camera (ADFOSC), and an image of celestial source obtained from the telescope (Pic: PIB)

Keeping in mind Prime Minister’s call to develop technology in all spheres, Indian scientists have indigenously designed and developed a low-cost optical spectrograph. This can locate sources of faint light from distant quasars and galaxies in a very young universe, regions around supermassive black-holes around the galaxies, and cosmic explosions.

Its worthwhile noting that the spectrograph is about 2.5 times less costly compared to the imported ones and can locate sources of light with a photon-rate as low as about 1 photon per second. The cost of this instrument is nearly Rs. 4 Crore.

The largest of its kind among the existing astronomical spectrographs in India, it has been successfully commissioned on the 3.6-m Devasthal Optical Telescope (DOT), located near Nainital, Uttarakhand. Interestingly, this spectrograph is not just the largest in the country but also Asia.

Till recent past, these costly spectroscopes were imported from abroad. This optical spectrograph named as Aries-Devasthal Faint Object Spectrograph & Camera (ADFOSC), has been indigenously designed and developed by Aryabhatta Research Institute of observational sciences (ARIES), Nainital. ARIES is an autonomous institute of Department of Science and Technology (DST), Government of India. Led by Dr. Amitesh Omar, ARIES scientist, the technical and scientific team, researched and developed various optical, mechanical, and electronics subsystems of the spectrograph and camera.

Astronomers worldwide use spectrograph to study distant quasars and galaxies in a very young universe, regions around supermassive black-holes around the galaxies, cosmic explosions like supernovae and highly energetic Gamma-ray bursts, young and massive stars, and faint dwarf galaxies.

Commending the effort, ARIES Director, Prof. Dipankar Banerjee observed, “The indigenous efforts to build complex instruments like ADFOSC in India is an important step to become ‘Aatmanirbhar’ in the field of astronomy and astrophysics.”

Effective collaboration

Besides ARIES, expertise from various national institutes, organizations, including the Indian Space Research Organization (ISRO) and some micro-small-medium-enterprises, was involved to review and build parts of the instrument serving as an example of effective collaboration. With this expertise, ARIES now plans to commission more complex instruments such as spectro-polarimeter and high spectral resolution spectrograph on the 3.6-m Devasthal telescope in the near future.

How the spectrograph works?

This instrument, a backbone of the 3.6-m DOT for observations of extremely faint celestial sources, uses a complex arrangement of several lenses made of special glasses, polished to better than 5-nanometer smoothness to produce sharp images of the celestial sky.

Photons coming from distant celestial sources, collected by the telescope, are sorted into different colors by the spectrograph and are finally converted into electronic recordable signals using an in-house developed Charge-Coupled Device (CCD) camera cooled to an extremely low temperature of -120 degree Celcius.