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Astronomers from Pune use updated GMRT to gauge mass of hydrogen in inaccessible galaxies

A group of cosmologists from the National Center for Radio Astrophysics (NCRA-TIFR) in Pune, and the Raman Research Institute (RRI), in Bangalore, utilized the overhauled Giant Metrewave Radio Telescope (GMRT) to quantify the nuclear hydrogen substance of worlds seen as they were 8 billion years prior, when the universe was youthful. This is the soonest age known to man for which there is an estimation of the nuclear gas substance of cosmic systems. This examination was distributed in the October 15, 2020 issue of the diary ‘Nature’.

“Galaxies in the universe are made up mostly of gas and stars, with gas being converted into stars during the life of a galaxy. Understanding galaxies thus requires us to determine how the amounts of both gas and stars change with time. Astronomers have long known that galaxies formed stars at a higher rate when the universe was young than they do today. 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 is unknown, mostly because we have had no information about the amount of atomic hydrogen gas, the primary fuel for star formation, in galaxies in these early times,” said Aditya Chowdhury, a Ph.D. student at NCRA-TIFR and the lead author of the study.

“We have, for the first time, measured the atomic hydrogen gas content of star forming galaxies about 8 billion years ago, using the upgraded GMRT. Given the intense star formation in these early galaxies, their atomic gas would be consumed by star formation in just one or two billion years. And, if the galaxies could not acquire more gas, their star formation activity would decline, and finally cease the observed decline in star formation activity can thus be explained by the exhaustion of the atomic hydrogen.” he added.

The estimation of the nuclear hydrogen mass of far off worlds was finished by utilizing the overhauled GMRT to look for a phantom line in nuclear hydrogen.

Not at all like stars which produce light emphatically at optical frequencies, the nuclear hydrogen signal lies in the radio frequencies, at a frequency of 21 cm, and must be distinguished with radio telescopes.

Sadly, this 21 cm signal is extremely feeble, and hard to identify from inaccessible individual universes even with incredible telescopes like the updated GMRT. To beat this impediment, the group utilized a procedure called ‘stacking’ to consolidate the 21 cm signs of almost 8,000 cosmic systems that had before been related to optical telescopes.

K S Dwarakanath of RRI and co-author of the study said, “We had used the GMRT in 2016, before its upgrade, to carry out a similar study. However, the narrow bandwidth before the GMRT upgrade meant that we could cover only around 850 galaxies in our analysis, and hence were not sensitive enough to detect the signal.”

“The big jump in our sensitivity is due to the upgrade of the GMRT in 2017. The new wide band receivers and electronics allowed us to use 10 times more galaxies in the stacking analysis, giving sufficient sensitivity to detect the weak average 21 cm signal.” said Jayaram Chengalur, of NCRA-TIFR, a co-author of the paper.

Distinguishing the 21 cm signal from the most removed worlds known to mankind was the fundamental science objective of the GMRT, when it was planned and worked by a group drove by eminent researcher and radio cosmologist Govind Swarup during the 1980s and 1990s.

“Govind Swarup was very interested in this work, and was following it keenly. Sadly, he passed away shortly before it was published. This work would not have been possible without him and the wonderful team that he put together to first build and then upgraded the GMRT,” said Nissim Kanekar of NCRA-TIFR, a co-author of the study.

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