A sample dwarf galaxy (small box left) observed with the Ultraviolet Imaging Telescope on AstroSat. AstroSat detected extremely blue star-forming clumps on the galaxy’s outer boundary (box on left)

(IUCAA)

Dwarf galaxies, made up of a few billion stars at most, have been the object of fascination for many astronomers. They offer a window into the evolution of the universe’s early galaxies. Studying star formation and assembly in these small, irregular galaxies can offer insights into how modern-day galaxies, like our own Milky Way Galaxy, evolved.

But observing BCDs in their developmental phase is extremely challenging since they remain very faint and faraway, lost in the infinite cosmos. Now, an international team of researchers have managed to track the birth of new stars on the periphery of these faraway dwarf galaxies using the Indian Ultra-Violet Imaging Telescope AstroSat—India’s first dedicated multi-wavelength satellite telescope designed to investigate celestial sources.

“Capturing the assembly process in dwarf galaxies is considered important because the diversity in their physical properties observed today challenge the current theoretical models of galaxy evolution. AstroSat/UVIT has been a remarkable addition to the list of UV observatories to date and has opened up promising windows to probe the understanding of the galaxy assembly process,” explains Anshuman Borgohain, an astronomer from Tezpur University, Assam, and lead author of the study.

Professor Kanak Saha at Pune’s Inter-University Centre for Astronomy and Astrophysics (IUCAA) conceived the study involving astronomers from India, the US and France. They have come one step closer to understanding how stars come to be in dwarf galaxies through this research. New stars in the distant dwarf galaxies, called Blue Compact Dwarf galaxies or BCDs, are known to migrate inwards towards their centre, contributing to the galaxies’ mass and volume.

Using AstroSat, the scientists discovered these star production zones in eleven BCDs! The findings of this research showed how “extended star formation” plays a role in the formation of dwarf galaxies.

“We are witnessing the ‘live’ formation of these far-way dwarf galaxies! AstroSat’s resolving power, and deep field imaging techniques have been the key to spotting some very young, large star-forming clumps. These form on the periphery and then spiral into the visible (optical) boundary of their galaxy within a billion years timescale, thus adding to the growth of the galaxy,” said Prof Saha.

Further, this study reports the discovery of extensive far-ultraviolet (FUV) discs in distant dwarf galaxies for the first time. To simply put it, our home-grown AstroSat detects far-off objects using ultraviolet, X-ray, and visible light, while NASA’s James Webb Space Telescope analyses distant galaxies in various infrared wavelengths.

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