India’s SARAS telescope gives clues to first stars, galaxies of universe

India’s SARAS radio telescope has helped scientists determine the properties of the earliest radio luminous galaxies formed 200 million years after the Big Bang, a period known as the Cosmic Dawn.

The findings, published in Nature Astronomy by an international group of scientists, provide an insight to the properties of the earliest radio loud galaxies that are usually powered by supermassive black holes.

A team of scientists, including Saurabh Singh from the Bengaluru-based Raman Research Institute (RRI), estimated the energy output, luminosity, and masses of the first generation of galaxies that are bright in radio wavelengths.

The Shaped Antenna measurement of the background Radio Spectrum 3 (SARAS) telescope — indigenously designed and built at RRI — was deployed over Dandiganahalli Lake and Sharavati backwaters in northern Karnataka in early 2020.

Scientists were able to look back in time just 200 million years after the Big Bang and provide new insight into the properties of galaxies at the time.

Besides RRI, researchers from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia, along with collaborators at the University of Cambridge and the University of Tel Aviv participated in the study to estimate the energy output, luminosity, and masses of the first generation of galaxies that are bright in radio wavelengths.

Scientists observed radiation from hydrogen atoms in and around the galaxies, emitted at a frequency of approximately 1420 MHz.

The radiation is stretched by the expansion of the universe, as it travels to us across space and time, and arrives at Earth in lower frequency radio bands 50-200 MHz, also used by FM and TV transmissions.

The cosmic signal is extremely faint, buried in orders of magnitude brighter radiation from our own Galaxy and man-made terrestrial interference, making its detection a challenge for astronomers.

The scientists have described how even non-detection of this line from the early universe can allow astronomers to study the properties of the very first galaxies by reaching exceptional sensitivity.

”The results from the SARAS 3 telescope are the first time that radio observations of the averaged 21-centimetre line have been able to provide an insight to the properties of the earliest radio loud galaxies that are usually powered by supermassive black holes,” said Ravi Subrahmanyan, former director of RRI and currently with Space & Astronomy CSIRO, Australia.