Representative image of a Galaxy.
(ESA / Hubble & NASA, A. Filippenko, R. Jansen)
Scientists from the Inter-University Center for Astronomy and Astrophysics (IUCAA), Pune have discovered one of the first galaxies in the universe, about 9.3 billion light-years from Earth. The breakthrough discovery, published on Monday, was made using AstroSat – India’s first multi-wavelength satellite.
Launched by the Indian Space Research Organization (ISRO) on September 28, 2015, and developed by several research institutes from India and Canada, it specializes in studying celestial sources simultaneously in X-ray, optical and UV spectral bands. It consists of five useful charges that help in capturing UV light coming from celestial objects.
The satellite, with its unique features, recently discovered an extreme ultraviolet light coming from the galaxy called AUDFs01. The discovery is expected to help our understanding of the first source of light in the universe.
Study UV radiation
The new galaxy was found in the area of the space called Hubble eXtreme Deep Field by AstroSat’s wide-field UltraViolet Imaging Telescope (UVIT). It is a small area based on the constellation Fornax, which was created using the data collected by the Hubble Space Telescope in 2003 and 2004. This part contains thousands of galaxies.
The research team observed and studied the UV light and the source for more than 28 hours in October 2016. However, it took nearly two years for the researchers to confirm that the emission originated from an early galaxy.
The universe expands, and that expansion extends light through space in a phenomenon known as cosmological redshift. The greater the redshift, the greater the distance that the light has traveled. As a result, telescopes with infrared detectors are needed to see light from the first, farthest galaxies.
(NASA, ESA, and L. Hustak)
The UV radiation that comes from distant celestial objects is difficult to detect from Earth, because most of it is absorbed by the planet’s atmosphere. Therefore, scientists need to use telescopes in space to make such discoveries.
According to reports, NASA’s Hubble Space Telescope (HST), which is larger than UVIT, could not detect UV emissions from this galaxy because the signals were too faint. AstroSat was able to successfully identify it because the background noise in the UVIT detector is relatively lower than the HST.
Importance of discovery
The authors of the study have noted that research is important in terms of strengthening our understanding of the early star systems of the universe that can only be found at extreme UV wavelengths. Studying the formation of early stars and galaxies helps to understand the conditions that lead to first rays of light or radiation after a long period of Cosmic Dark Age in the early universe after the Bing Bang.
A schematic sketch of cosmic history.
(NASA / WMAP Science Team)
Scientists believe that shortly after the big bang it reached its highest temperature and slowly began to cool. During this time it consisted mostly of subatomic particles such as protons, neutrons and photons. Over time, these neutrons and protons combine to form deuteron and helium, which attracted electrons and eventually fused to neutral hydrogen.
Theoretically, at this very point, with the help of these ancient elements, the first light arose and was allowed to run freely in all directions in space. However, more than 200 million years after the Big Bang, there were no stars, galaxies or other celestial objects.
Cosmic dark time refers to a short time when the universe was completely dark, and it finally came to an end when the first generation of stars began to form again. This further resulted in the splitting of atoms into protons and electrons leading to the reionization of the universe. What processing resulted in this reunion, however, remains a mystery. And now UVIT detection of extreme UV emissions offers an unexpected hope for solving this mystery.
Detection of extreme radiation
The research paper states: “One of the striking problems of today’s observing cosmology is the understanding of the nature of sources that produced most of the ionizing radiation after the cosmic dark age.” It further adds: “Direct detection of these sources for reionization is practically unattainable at high redshift due to the steep decline in transmission of intergalactic medium.”
Artist impression presents the early universe.
(ESA / Hubble, M. Kornmesser and NASA)
The photons emitted by such reionization sources in the early universe are hindered by light-blocking material such as carbon, as intergalactic medium. Therefore, with the current level of knowledge and technology, it is impossible to observe such radiation from the Earth.
Fortunately, some radiation reaches our space telescopes and this has been studied through this research. According to reports, this is the first time a galaxy has been observed in the extreme ultraviolet light and will further help to shed light on the conditions of the early universe. The research team was led by Dr. Kanak Saha, University Professor of Astronomy at IUCAA, and consists of international researchers from Switzerland, France, the US, Japan and the Netherlands.
The study was published earlier this week in the journal Nature Astronomy and is accessible over here.
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