Astronomers had lengthy recognized that galaxies shaped stars sooner when the universe used to be younger than they do these days.
Using the upgraded Giant Metrewave Radio Telescope (GMRT), astronomers from the National Centre for Radio Astrophysics (NCRA-TIFR) in Pune, and the Raman Research Institute (RRI), had measured the atomic hydrogen content material of galaxies noticed as they had been Eight billion years in the past when the universe used to be younger.
For the first time, astronomers have measured the atomic hydrogen gas content material of star-forming galaxies about Eight billion years in the past. Given the intense megastar formation in those early galaxies, their atomic gas could be fed on by way of megastar formation in only one or two billion years. It way, the universe does no longer have a limiteless amount of gasoline to proceed making stars ceaselessly.
Aditya Chowdhury, a Ph.D. scholar at NCRA-TIFR and the lead writer of the find out about, mentioned, “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.”
Using GMRT, astronomers looked for a spectral line in atomic hydrogen. Unlike stars, which emit mild strongly at optical wavelengths, the atomic hydrogen sign lies in the radio wavelengths, at a wavelength of 21 cm, and will only be detected with radio telescopes. Unfortunately, this 21 cm sign is very susceptible and hard to look from far-off particular person galaxies, even with tough telescopes like the upgraded GMRT.
To triumph over this limitation, the group used a methodology referred to as “stacking” to mix the 21 cm indicators of just about 8,000 galaxies that had previous been known with optical telescopes. This means measures the moderate gas content material of those galaxies.
Okay. S. Dwarakanath of RRI, a co-author of the find out about, discussed, “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.”
Jayaram Chengalur, of NCRA-TIFR, a co-author of the paper, mentioned, “The big jump in our sensitivity is due to the upgrade of the GMRT in 2017. The new wideband receivers and electronics allowed us to use ten times more galaxies in the stacking analysis, giving sufficient sensitivity to detect the weak average 21 cm signal.”
Chowdhury, A., Kanekar, N., Chengalur, J.N. et al. H I 21-centimeter emission from an ensemble of galaxies at a median redshift of one. Nature 586, 369–372 (2020). DOI: 10.1038/s41586-020-2794-7