SE Valley Times

NASA's James Webb Space Telescope (JWST) has achieved a significant milestone by capturing images of over 40 individual stars in a galaxy nearly 6.5 billion light-years away. This discovery, published in Nature Astronomy, was made possible through the use of gravitational lensing and JWST's advanced capabilities.

The team of astronomers, led by Yoshinobu Fudamoto from Chiba University and including Arizona State University co-authors Seth Cohen, Nicholas Foo, and Rogier Windhorst, observed this distant galaxy when the universe was half its current age. "I'm amazed at all the different ways gravitational lensing has become a useful tool to study different astrophysical phenomena," said Cohen.

This achievement marks a record-breaking number of individual stars detected in the distant universe and provides an opportunity to explore dark matter. Windhorst remarked on the unexpected success: "When we predicted in 2018 that stars in galaxies at cosmological distances might be observed with Webb individually... I never dreamed of Webb seeing them in such large numbers."

Gravitational lensing allows astronomers to see these distant stars by magnifying their light through massive objects' gravitational fields. "To us, galaxies that are very far away usually look like a diffuse, fuzzy blob," said Fudamoto. The process involves combining two gravitational lenses for necessary magnifications: a macrolens created by dark matter halos and microlenses formed by unbound stars within galaxy clusters.

In December 2022 and 2023, JWST captured images of the Dragon Arc galaxy behind Abell 370 cluster. Astronomers identified 44 individual stars whose brightness varied due to gravitational lensing effects. "This groundbreaking discovery demonstrates... that studying large numbers of individual stars in a distant galaxy is possible," said Fengwu Sun.

The discovery relied on serendipitous alignments with floating stars acting as additional microlenses within the galaxy cluster. Co-author Eiichi Egami explained how these unbound stars contribute to increased magnification: "When one of them happens to pass in front of the background star... it acts as a microlens."

The findings illustrate new possibilities for studying stellar populations across vast cosmic distances using advanced technology and natural phenomena like gravitational lensing.