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Updated: Aug 25, 2020 11:02:28 AM
This is a very important clue to the end of the dark ages of the Universe and of light in the Universe, said Dr Somak Raychaudhury, director of IUCAA. (Representation)
In a major breakthrough, a global team led by scientists from the Interuniversity Center for Astronomy and Astrophysics (IUCAA) discovered one of the first galaxies in extreme ultraviolet light. AstroSat, India’s first multi-wavelength satellite with five unique X-ray and UV telescopes working in tandem, detected extreme ultraviolet light from a galaxy called AUDFs01, 9.3 billion light-years from Earth.
The discovery was made by an international team of astronomers led by Dr. Kanak Saha, associate professor of astronomy at IUCAA, and was published on August 24 by Nature Astronomy. The team includes scientists from India, Switzerland, France, the United States, Japan and the Netherlands.
Dr Saha told the Indian Express that the team observed the galaxy, located in the Extreme Deep field, via AstroSat. These observations lasted for more than 28 hours in October 2016. But it has taken nearly two years since then to carefully analyze the data to make sure the emission is indeed coming from the galaxy.
This is a very important clue to the end of the dark ages of the Universe and of light in the Universe, said Dr Somak Raychaudhury, director of IUCAA. “We have to know when it started, but it was very difficult to find the first sources of light,” he said.
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Since UV radiation is absorbed by the Earth’s atmosphere, it must be observed from space. Previously, NASA’s Hubble Space Telescope (HST), which is significantly larger than the Ultraviolet Imaging Telescope (UVIT) on Astrosat, did not detect any UV emissions (with energy greater than 13.6 eV) of this galaxy because it is too weak.
“AstroSat / UVIT was able to achieve this unique feat because the background noise of the UVIT detector is much lower than that of the HST,” said Dr Saha.
He added: “We knew it would be a daunting task to convince the international community that UVIT recorded ultraviolet emissions from this galaxy while the more powerful HST did not… this discovery of AUDFs01 by AstroSat demonstrates that there is hope and maybe, this is the beginning “.
A statement released by the IUCAA explained that after the Big Bang, the Universe was a hot soup of particles (i.e. protons, neutrons, and electrons). As the universe began to cool, protons and neutrons began to combine into ionized hydrogen atoms (and eventually helium). These ionized atoms of hydrogen and helium attracted electrons, turning them into neutral atoms – which allowed light to travel freely for the first time, since this light no longer scattered free electrons. The universe was no longer opaque. But there were no stars or galaxies, and the Universe was dark.
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A little later, perhaps a few hundred million years after the Big Bang, the Dark Ages ended when the first stars and galaxies formed and the energy emerging from them ionized hydrogen and l helium, again dividing atoms into protons and electrons – this is the time of reionization.
Astronomers searched for sources that reionized the early universe. The usual suspects were the first astronomical objects, especially small newborn galaxies. But observing ionizing radiation from these sources is practically impossible. The probability that a fraction of ultraviolet photons will escape from the host galaxy and be captured by a telescope on Earth is practically zero, as these photons will be absorbed by the gas in the galaxy or the gas surrounding the galaxy or the matter between them. galaxies and us.
How some of these high energy photons manage to cross all barriers and reach Earth is a mystery. The absorption in the intergalactic medium is so severe that it is impossible to directly observe the ionizing photons at the time of reionization.
“In the last epoch, intergalactic absorbers are decreasing and we have a chance to detect such photons, but it’s still like a lottery,” said co-author Dr Akio Inoue, professor at Waseda University in Japan.
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