Giant Metrewave Radio Telescope

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Why in news?

Scientists have expressed apprehension that the proposed Rs 16,000-crore Pune-Nashik high-speed rail project could jeopardise the operations of the Giant Metrewave Radio Telescope (GMRT) near Pune.

GMRT is a low-frequency radio telescope that helps investigate various radio astrophysical problems ranging from nearby solar systems to the edge of the observable universe.
Located at Khodad, 80 km north of Pune, the telescope is operated by the National Centre of Radio Astrophysics (NCRA).
- NCRA is a part of the Tata Institute of Fundamental Research (TIFR), Mumbai.
- GMRT is a project of the Department of Atomic Energy (DAE), operating under the Tata Institute of Fundamental Research (TIFR).
It consists of 30 fully- steerable dish type antennas of 45-meter diameter each, spread over a 25-km region.
- GMRT is presently the world’s largest radio telescope operating at meter wavelength.

Although GMRT will be a very versatile instrument for investigating a variety of radio astrophysical problems, two of its most important astrophysical objectives are:
- to detect the highly redshifted spectral line of neutral Hydrogen expected from protoclusters or protogalaxies before they condensed to form galaxies in the early phase of the Universe and
  - Redshift represents the signal’s wavelength change depending on the object’s location and movement.
- to search for and study rapidly-rotating Pulsars in our galaxy.
  - Pulsars are rapidly rotating neutron stars with extremely high densities.

Highly sought-after telescope
- GMRT is a unique facility functioning within the frequency bandwidth of 100 Mhz-1,500 MHz.
- It is a highly sought-after telescope both within India and by scientists from 30-plus countries.
Understanding the evolution of galaxies over cosmic time
- Understanding the evolution of galaxies over cosmic time requires tracing the evolution of neutral gas at different cosmological periods.
  - Atomic hydrogen is the basic fuel required for star formation in a galaxy.
  - When hot ionised gas from the surrounding medium of a galaxy falls onto the universe, the gas cools and forms atomic hydrogen.
  - This then becomes molecular hydrogen and eventually leads to the formation of stars.
  - Atomic hydrogen emits radio waves of 21 cm wavelength, meaning the wavelength is a direct tracer of the atomic gas content in nearby and distant galaxies.
- However, this radio signal is feeble and nearly impossible to detect the emission from a distant galaxy.
- Using GMRT data, recently scientists detected signal that was emitted from a distant galaxy when the universe was only 4.9 billion years old.
Galactic and extragalactic radio sources
- Because of its large collecting area and wide frequency coverage, GMRT is an useful instrument for studying many other problems at the frontiers of astrophysics.
- These include studies of Solar and planetary radio emissions; relationship between Solar activity and disturbances in the interplanetary medium etc.

The Ministry of Railways gave ‘in-principle’ approval to the Pune-Nashik high-speed rail project.
- The high-speed railway line will cover a distance of 235 km in under two hours.
- As per the proposal, trains will run at a speed of 200 km/hr.
It is being feared that this project could jeopardise the operations of the Giant Metrewave Radio Telescope (GMRT).
Radio noise and interference from this rail project might affect the working of GMRT.
- A majority of the dish antennas of GMRT come within unacceptably close range of the railway line.