Context: A team of astronomers from the Pune-based National Centre for Radio Astrophysics (NCRA-TIFR) and Raman Research Institute (RRI) in Bengaluru have used the upgraded Giant Metrewave Radio Telescope (GMRT) to measure the atomic hydrogen content of galaxies seen as they were eight billion years ago when the universe was young.


  • Clouds of gas are common in our galaxy and in other galaxies like ours. These clouds are called nebulae. 
  • The majority of the gas in nebulae consists of molecules of hydrogen and helium.
  • A star is born when atoms of light elements are squeezed under enough pressure for their nuclei to undergo fusion reaction.
  • Understanding galaxies requires us to determine how the amounts of both gas and stars change with time. 
  • The star formation activity in galaxies peaked about 8-10 billion years ago and has been declining steadily till today
  • The cause of this decline was unknown as there had been no information regarding the amount of atomic hydrogen gas — the primary fuel for star formation — in galaxies in these early times.

Significance of the discovery:

  • The scientists have, for the first time, measured the atomic hydrogen gas content of star forming galaxies about 8 billion years ago.
  • The observed decline in star formation activity could thus be explained by the exhaustion of the atomic hydrogen as Hydrogen is consumed while star formation and during fusion reaction.
  • 21 cm signal: Unlike stars which emit light strongly at optical wavelengths, the atomic hydrogen signal lies in the radio wavelengths, at a wavelength of 21 cm, and can only be detected with radio telescopes.
    • Detecting the 21 cm signal from the most distant galaxies in the universe was the main science goal of the GMRT, when it was designed by a team led by the late pioneering astrophysicist Govind Swarup in the 1980s and 1990s.

Giant Metrewave Radio Telescope (GMRT)

  • The GMRT is a radio telescope located in Pune, India. 
  • It is operated by the National Centre for Radio Astrophysics (NCRA), a part of the Tata Institute of Fundamental Research (TIFR), Mumbai. 
  • It comprises a group of dishes or an “array” that are all steerable and can turn their giant heads in any direction.. 
  • This type of operation, where multiple antennae operate as one, is called interferometry.


Image source: DNA India