A Telescope of Smart Design
The Giant Metrewave Radio Telescope (GMRT) is an array of thirty fully steerable parabolic dishes, each 45 metres in diameter. The facility is located about 80 km north of Pune, India. The antennas are arranged in a 'Y' configuration, with twelve dishes forming a compact central array about 1-by-1 kilometer in size, and the remaining eighteen spread out along three 14-kilometer-long arms. This layout gives the telescope a total baseline distance of up to 25 kilometers, allowing for both high-resolution imaging of small objects and the sensitivity to detect large, diffuse structures.
An important innovation in the GMRT's construction was the 'SMART' concept, which stands for Stretch Mesh Attached to Rope Trusses. Instead of a conventional heavy backup structure, the dish surface is made of a lightweight stainless steel wire mesh held in shape by a series of rope trusses. This design significantly reduced the weight and cost of the antennas, making it possible to build such a large array economically. The total collecting area is nearly 30,000 square meters. The telescope operates at several frequency bands between 150 and 1500 MHz, specializing in the metre-wavelength part of the radio spectrum.
Probing the Cosmic Dawn
One of the principal scientific goals for the GMRT is to detect faint signals from the Epoch of Reionization (EoR). This period, which started a few hundred million years after the Big Bang, marks the time when the first stars and galaxies formed, and their radiation began to ionize the neutral hydrogen that filled the universe. The GMRT searches for the highly redshifted 21-cm line radiation from this primordial hydrogen gas. Observing this signal allows astronomers to map the structure of the early universe and understand how the first luminous objects came into being.
The GMRT is also a versatile instrument used by astronomers worldwide to study a wide variety of celestial objects. Its observations cover pulsars, supernovae, galaxies, and quasars. In 2020, it helped observe the largest explosion known in the history of the universe, originating from the Ophiuchus Supercluster. In 2023, it detected a radio signal from neutral atomic hydrogen that originated 8.8 billion light-years away. The telescope has also been used to create the TIFR GMRT Sky Survey (TGSS), which has mapped about 90% of the sky at a frequency of 150 MHz.