Guwahati: Anshuman Borgohain, a research scholar at Tezpur University was part of an international first-of-its-kind study that discovered that new stars are forming beyond the visible boundaries of a sample of distant Blue Compact Dwarf (BCD) galaxies situated about 1.5 – 3.9 billion light-years away from Earth.

The discovery was a joint outcome of a study by an international team of astronomers from India, the USA and France, conceived using the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat, India’s first dedicated multi-wavelength space observatory.

Anshuman Borgohain was the lead author of a research article on the study that was published in the renowned multidisciplinary science journal Nature on 20 July 2022.

Anshuman is working under the joint supervision of Dr Rupjyoti Gogoi at Tezpur University and Prof. Kanak Saha at IUCAA.

 “It is still unclear how dwarf galaxies of the past have evolved into the ones in the present day. Hence, capturing their assembly process over the cosmic ages is considered as one of the important links to complete the picture of galaxy formation and evolution,” Anshuman said.

He also commended AstroSat/UVIT’s imaging capabilities and said, “It is opening up promising avenues in the field of extragalactic astronomy”.

Dr Rupjyoti Gogoi, co-author, Assistant Professor of Physics at Tezpur University and associate at IUCAA said, “The current work is an inspiration to young researchers of the country as this utilizes data from India’s indigenous satellite, AstroSat.”

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“This also showcases the glorious association of IUCAA and a university, which surely will motivate the researchers working in Indian Universities. We look forward to enhancing this collaborative endeavour between IUCAA and Tezpur University,” Gogoi said.

Prof. Kanak Saha, the co-author of the article and Professor of Astronomy at IUCAA, who conceived the study, said, “The resolving power of UVIT and UV deep field imaging techniques have indeed been the key to spotting these very young, faint and large star-forming clumps.”

He mentioned that it would not have been possible to detect these faraway clumps at slightly larger distances from us and that we do not have such an example in present-day dwarf galaxies.

The background is a 3-color optical image taken by the Hubble Space Telescope. The small box (left) shows a sample dwarf galaxy that was observed with the Ultraviolet Imaging Telescope on AstroSat.

AstroSat detected extremely blue star-forming clumps on the galaxy’s outer boundary (3-color UV-optical image shown in zoomed-in box).

Dr. Bruce Elmegreen, who contributed to the study, is a principal research staff in the IBM Research Division, USA.

He said, “It has been a mystery how some small galaxies like these can have such active star formation.”

He explained that these observations point to the funnelling of outer accreting gas further inwards due to gravitational forces exerted by massive outer clumps.

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“The discovery teaches us how surprisingly the star formation can proceed in relatively pristine low-metallicity gas”, said Prof. Francoise Combes of Observatoire de Paris, France, another co-author, and Professor at the College de France.

Prof. Shyam Tandon, another co-author of this study and ex-emeritus Professor at IUCAA, has wondered whether these stellar clumps could have been sources of Lyman continuum photons, which ionise the neutral hydrogen gas.

“Understanding the birth and fate of the cosmos has been an ever-fascinating puzzle for humankind. The discovery of such unseen phenomena in these distant dwarf galaxies is just another piece of the puzzle and a glimpse of the unknown that new state-of-the-art observatories are starting to show and have to offer in near future,” Tezpur University Vice Chancellor Prof. Vinod K. Jain said.

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