Indian Satellite Discovers One of the Earliest Galaxies

In a major development, one of the earliest galaxies has been discovered by a global team of scientists using India’s first multi-wavelength satellite AstroSat. This discovery was published in the science journal Nature Astronomy on August 24.

AstroSat has five unique X-ray and ultraviolet telescopes working in tandem, and has detected extreme UV light from a galaxy 9.3 billion light-years away from Earth. 

The breakthrough was made by an international team of astronomers—comprising scientists from India, Switzerland, France, USA, Japan, and the Netherlands—led by Dr Kanak Saha, associate professor of astronomy at Inter-University Centre for Astronomy and Astrophysics (IUCAA) located in Pune in the south-western state of Maharashtra in India. 

The team observed the galaxy, through AstroSat back in October 2016, for over 28 hours, Saha told The Indian Express. It is located in the eXtreme Deep field—the patch of sky which consists of thousands of galaxies which was constructed combining 10 years of NASA Hubble Space Telescope photographs in 2012, making it the deepest photo of the universe at that time. It took them nearly two years to analyse the data to confirm that the emission was indeed from the galaxy.

This is an important clue to how the dark ages of the Universe ended and there was light in the Universe, said Dr Somak Raychaudhury, the director of IUCAA in a statement released by the university. “We need to know when this started, but it has been very hard to find the earliest sources of light,” he said.

Since UV radiation is absorbed by Earth’s atmosphere, it has to be observed from space. Earlier, NASA’s Hubble Space Telescope (HST), significantly larger than the UVIT (UV Imaging Telescope), did not detect any UV emission from this galaxy because the emission was too faint. “AstroSat/UVIT was able to achieve this unique feat because the background noise in the UVIT detector is much less than the ones on HST,” said Saha. “We knew it would be an uphill task to convince the international community that UVIT has recorded extreme-UV emission from this galaxy when the more powerful HST has not… this discovery of AUDFs01 by AstroSat establishes that there is hope and perhaps, this is the beginning”.

One of the outstanding problems of current observational cosmology is to understand the nature of sources that produced the bulk of the radiation after the Cosmic Dark Age—the dark period after the Big Bang before the earliest stars were born. Scientists have been trying to figure out the earliest sources which re-ionised the early universe. However, that observation has been near difficult because the extreme-UV photons which emanate from such sources don’t reach the telescope and are absorbed by the gas and matter in the host galaxy.

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