According to a recent study, signals from the outskirts of a galaxy no older than 150 million years indicate the formation of newer stars in galaxies beyond their visible boundaries. The research follows how these young stars, found in the form of star-forming complexes or clusters, migrate into the inner regions and gradually build up the stellar content of these galaxies. Astrophysicists have studied how galaxies, the basic building blocks of our universe, form and evolve into what they are today. But the picture still remains incomplete.
The UltraViolet Imaging Telescope (UVIT) aboard AstroSat, India’s first dedicated multi-wavelength space observatory, recently detected faint Far UltraViolet (FUV) light emission at the edge of a sample of distant Blue Compact Dwarf (BCD) galaxies that are about 1.5. – 3.9 billion light years away. These are small galaxies that are usually characterized by their centrally concentrated star formation.
The discovery, the joint result of a study by an international team of astronomers from India, the US and France, is a significant step towards tracking down the mysteries of galaxy formation. The study published in the journal Nature was designed by Prof. Kanak Saha of the Inter University Center for Astronomy and Astrophysics (IUCAA), Pune. Anshuman Borgohain, lead author of the paper and recipient of an INSPIRE Fellowship of the Department of Science and Technology (DST), said the appearance of such young stars on the periphery of galaxies is usually a telltale signature of recent gas. accretion from their surroundings, which drives the formation of stars and the subsequent growth of galaxies.
The researcher at Tezpur University worked under the joint supervision of Dr. Rupjyoti Gogoi, Assistant Professor of Physics, Tezpur University, and Professor Kanak Saha, Professor of Astronomy, IUCAA.”The resolving power of UVIT and deep-field UV imaging techniques was the key to observing these very young, large star-forming clusters. Due to their great distance from us, it was a challenging task to detect these faint, extremely blue star-forming clusters with millions of solar masses,” said the professor Kanak Saha and emphasized that it helped to witness the “live” formation of these distant dwarf galaxies.
Dr. Bruce Elmegreen, principal research team at IBM Research Division, USA, who contributed to the study, said: “It was a mystery how some small galaxies like these could have such active star formation. These observations suggest that gas accreting in the distant outer parts may be forced inward by the torque exerted by the giant gas and stellar complexes. This migration creates a central density during the lifetime of the galaxy.”
Co-author Prof. Francoise Combes of the Observatoire de Paris, France, a professor at the College de France, explained that the discovery illustrates how surprisingly star formation can take place in relatively pristine, low-metallicity gas. “The outer parts of these gaseous disks are unstable to fragmentation, although these dwarfs must be dominated by dark matter to limit fragmentation,” she explained. Co-author Prof. Shyam Tandon, former professor emeritus at IUCAA and PI from UVIT, emphasized the importance of UVIT data in this study. Dr. Rupjyoti Gogoi, an assistant professor of physics at Tezpur University and an IUCAA collaborator, said the work, which uses data from India’s indigenous AstroSat satellite, could be an inspiration for young researchers in the country, while Prof. Somak Raychaudhury, director from IUCAA Pune and Prof. Vinod K. Jain, Vice-Chancellor of Tezpur University, highlighted the benefits of such collaboration.
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