It was in 1895 that a young scientist by the name of Jagadish Chandra Bose first demonstrated that radio waves could be generated and received by man-made equipment. This was a momentous achievement, which was closely followed by the efforts of the likes of Guglielmo Marconi to harness it into practical and commercially usable devices. Thus was born the telecom revolution, without whose products we can not imagine our lives today.
In 2012, the IEEE (Institute of Electrical and Electronics Engineers) — the largest body of professionals in the world, which is dedicated to the promotion of technology — decided to honour this achievement of Acharya J C Bose with the prestigious ‘IEEE Milestone’ status (along with the 1928 Nobel Prize-winning discovery of Raman Effect by Sir C V Raman). This status is conferred by the IEEE to select achievements in science and technology that have had a major international or regional impact.
However, astronomers did not realise that this development of radio technology could have any significant impact on the study of the Universe, till the serendipitous detection of radio emission coming from celestial objects in our galaxy by Karl Jansky, a young engineer working at Bell Labs, USA, in 1931. This discovery opened up a new window to the study of the Universe: Radio Astronomy, which has, over the years since, vastly improved our understanding of the cosmos.
Radio astronomy came to India with the setting up of the radio astronomy group at the Tata Institute of Fundamental Research (TIFR) in 1963, by a young scientist by the name of Govind Swarup. The group started with building first the relatively modest Kalyan Radio Telescope in 1965 for studies of the Sun, followed by the significantly more ambitious Ooty Radio Telescope (ORT) in 1970, which established the credentials of the group. By 1980, they had expanded this to the Ooty Synthesis Radio Telescope.
Following this, Prof Govind Swarup and his team proposed the setting up of a truly international class radio observatory: the Giant Metrewave Radio Telescope (GMRT). Conceived in 1985, and approved in 1988, the GMRT proposed an array of 30 numbers of 45 metre diameter fully steerable parabolic dishes, spread out over a region of almost 30 km in diameter, at a site located about 80 km from Pune. The prime motivation was to explore important aspects of the Universe that are best studied at metre wavelengths. Hence, the frequency coverage of the GMRT array was chosen to go from wavelengths of about 20 cm (1500 MHz) to about 2 m (around 150 MHz). To build the GMRT, the group shifted headquarters to Pune and set up the National Centre for Radio Astrophysics (NCRA).
After completion of acquisition of the land in 1990, work on the construction of the GMRT started in 1991, and the first antenna was erected in 1993. Construction of all the 30 antennas was completed by 1995, even as construction and commissioning activities for the different receiver systems continued alongside. Regular astronomical observations started in 1997, and the first publication of results from the GMRT in an international journal happened in 1999. In October 2001, the GMRT was formally declared an international facility, available for use by astronomers from all over the world.
In the process of its indigenous design and construction, the GMRT pioneered quite a few new and innovative ideas, while overcoming some significant technological challenges. It was one of the first radio astronomy observatories to replace radio communication links with optical fibre technology to connect the antennas in the array to the central processing facility, a feature that is now almost routine in all modern radio observatories. It was also one of the first interferometric array telescopes to also have a dedicated phased array mode to support observations of compact objects like pulsars. The design of the GMRT employed innovative ideas like SMART (Stretched Mesh Attached to Rope Trusses) to build very large fully steerable antennas (45 metres in diameter) that are very light (only about 100 tons) and hence very economical, while still providing the required accuracy and efficiency.
The design of the electronics for the GMRT was very challenging, all the way from the radio frequency front-end electronics at each antenna, to the back-end digital signal processing system at the central receiver building; but the in-house teams rose to the challenge and were able to deliver all these systems successfully.
All of this resulted, by the early 2000s, in the creation of the largest and most sensitive low frequency radio telescope in the world — a position that the GMRT has maintained over the years. The next generation at NCRA has further enhanced the capabilities of the GMRT with a major technological upgrade carried out during 2012 – 2018 that will keep it on the forefront on the global scene.
Over the years, the GMRT has seen users from more than 40 different countries carry out a range of interesting experiments. The competition for observing time on the GMRT is tough, and only the best science proposals get accepted by the review committee. This exemplifies how much the GMRT is sought after by the national and international community for cutting-edge exploration of the Universe and how it has built up its reputation and trust over the years.
The GMRT has produced several new and interesting scientific results and discoveries in more than 20 years of its operation. Presently, around 40-50 papers based on data from the GMRT are published in international journals every year. The range of science addressed is vast, covering many diverse topics: the Sun, radio stars, as well as exotic neutron stars (called pulsars); supernova remnants and other nebulae, distribution of hydrogen gas in our galaxy; studies of other galaxies (including clusters of galaxies) and their evolution over cosmic time; various kinds of transient, explosive events in the Universe; the early Universe when the first stars and galaxies were formed; survey of the entire sky to make one of the most sensitive all-sky atlas at low frequencies.
In addition, the GMRT has also been used for interesting experiments in space science: for tracking critical space missions such as the landing on Mars by the Schiaparelli probe from the Exomars mission of the European Space Agency, in 2016. For this, NCRA worked in collaboration with NASA and ESA to harness the sensitivity of the GMRT to pick up the signal (of strength similar to what a typical mobile phone transmits) from the probe as it made its descent through the Martian atmosphere.
On the socio-technical front, in addition to leading to a renaissance of low frequency radio astronomy in the world, the GMRT has also led to a major growth of professional astronomy in India, while also spurring the growth of a vast range of technology and capability growth in the country. A large number of students and scientists have been trained on the GMRT to become world class astronomers, and a strong engineering team has grown around the construction, maintenance and upgrade of the facility.
In November 2020, the IEEE approved the proposal to accord the ‘IEEE Milestone’ status to the GMRT. The dedication ceremony for this was held on March 30, 2021. It was a proud moment not just for the NCRA family, but for the entire science and technology fraternity of the country to see a modern, world-class, made-in-India facility get this prestigious recognition at the global level. It is also a fitting tribute to the pathbreaking work of Acharya J C Bose that earned the first ‘IEEE Milestone’ in India. This special recognition to the GMRT will surely motivate the current as well as future generations to reach for even higher goals, be it for domestic projects like further expanding the GMRT or building other facilities in the country, or for confidently taking India into active participation in large international projects.
One of the most attractive next generation projects in radio astronomy that India is looking at is the Square Kilometre Array (SKA). The SKA aims to build an observatory that is several times more powerful than the GMRT that promises to revolutionise our view of the Universe. It is a truly collaborative project of many nations — as many as a dozen countries at present — putting together their skills and resources to achieve the larger common goal. India is one of the nations involved in the SKA from the initial stages, and has made significant contributions in the early planning and design phases. Much of this has been made possible due to the experience and confidence gained from building facilities like the ORT and GMRT in the country. Looking to the future, India is well-poised to make substantial contributions to the construction of the SKA and to take its due place in the comity of nations in the arena of modern radio astronomy.
*The writer is Centre Director, National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune.
