James Webb Telescope captures tiny galaxies that reveal big secret

India Today

13-06-2025

Using data from NASA's James Webb Space Telescope (JWST), astronomers have identified dozens of small, starburst galaxies that played a pivotal role in transforming the early universe during a period known as cosmic reionisation.These tiny galaxies, though small in size, emitted powerful ultraviolet light that helped clear the fog of neutral hydrogen gas enveloping the universe's first billion years, enabling the universe to become transparent and evolve into its current state.advertisementThe discovery, presented by Isak Wold, an assistant research scientist at Catholic University of America and Nasa's Goddard Space Flight Center, was made possible by the unprecedented sensitivity of JWST's instruments, particularly the Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec).
The team analysed images from the UNCOVER observing program, which focused on the massive galaxy cluster Abell 2744, also known as Pandora's cluster. This cluster's immense gravity acts as a natural lens, magnifying distant galaxies and extending Webb's observational reach about 4 billion light-years away.The galaxies identified date back to when the universe was roughly 800 million years old, an epoch astronomers call redshift 7.During this time, vigorous star formation episodes—starbursts—occurred in these low-mass galaxies, producing intense ultraviolet radiation. This radiation ionised the surrounding hydrogen gas by stripping electrons from atoms, a process essential for the universe's transition from opaque to transparent.advertisementThe researchers detected a distinctive green emission line from doubly ionised oxygen, originally visible light stretched into the infrared spectrum due to cosmic expansion, confirming the presence of these energetic processes.
The project mapped a giant galaxy cluster known as Abell 2744, nicknamed Pandora's cluster. (Photo: Nasa)
'These galaxies punch well above their weight,' said Wold. To build a galaxy with the stellar mass of our Milky Way, one would need between 2,000 and 200,000 of these small galaxies. Yet, their abundance and ultraviolet output are sufficient to account for the entire reionisation process, assuming they release ultraviolet light at efficiencies similar to comparable galaxies in the present universe.This finding sheds light on a longstanding cosmic mystery about what powered reionisation, emphasising the outsised role of small, star-forming galaxies in shaping the universe's early evolution.The James Webb Space Telescope continues to revolutionise our understanding of cosmic history by revealing the building blocks of galaxies from the dawn of timeMust Watch