Looking deep into the cosmos and expecting to isolate individual stars in galaxies billions of light-years away has long been considered nearly impossible in astronomy. Such an endeavor is akin to attempting to discern individual grains of dust within craters on the Moon using a pair of binoculars. However, thanks to a remarkable interplay of natural phenomena and advanced technology, an international team of astronomers has defied expectations, making a groundbreaking discovery that reshapes our understanding of the universe.
Using NASA’s James Webb Space Telescope (JWST), a state-of-the-art instrument that continues to revolutionize space observation, postdoctoral researcher Fengwu Sun from the Center for Astrophysics | Harvard & Smithsonian (CfA) and his team managed to peer into a galaxy located nearly 6.5 billion light-years from Earth. This galaxy existed at a time when the universe was only about half of its current age. In a feat made possible by the combined power of gravitational lensing and JWST’s advanced capabilities, the team identified 44 individual stars within this distant galaxy. This achievement, unprecedented in its scope, marks the largest number of individual stars ever observed in such a remote corner of the cosmos.
Published in the prestigious journal Nature Astronomy, the discovery sets a new benchmark in the field of astrophysics. Beyond breaking records, it opens the door to new avenues of exploration, particularly regarding one of the universe’s greatest mysteries—dark matter. As Fengwu Sun noted, this work provides a way to study individual stars in distant galaxies at a scale previously deemed unattainable. Earlier efforts using the Hubble Space Telescope had identified a mere seven stars under similar circumstances. JWST’s capabilities, coupled with gravitational lensing, have now exponentially increased the number of resolvable stars, heralding a new era in extragalactic astronomy.
Sun and his team focused their attention on a celestial feature known as the Dragon Arc. This galaxy lies behind a massive cluster of galaxies, Abell 370, which acts as a natural magnifying glass through a phenomenon called gravitational lensing. As light from the Dragon Arc passes near Abell 370, the gravitational fields of the cluster bend and amplify it, stretching the distant galaxy into an elongated, mirror-like image. This “hall of mirrors” effect enabled JWST’s instruments to distinguish individual stars within the Dragon Arc that would otherwise remain undetectable.
Analyzing the light emitted by these stars, the team uncovered fascinating details. Unlike prior findings, which primarily identified blue supergiant stars resembling Rigel and Deneb—among the brightest in the night sky—the Dragon Arc’s stellar population revealed a dominance of red supergiants. These are cooler, massive stars in the final stages of their life cycle, akin to Betelgeuse in the Orion constellation. Such a discovery highlights JWST’s exceptional ability to detect stars at lower temperatures through its sensitivity to infrared light, a capability that sets it apart from its predecessors.
The implications of this discovery extend beyond merely cataloging distant stars. It provides critical insights into the types of stars that populated galaxies when the universe was much younger and helps refine our understanding of stellar evolution. Red supergiants, while extensively studied in closer galaxies, offer unique opportunities to investigate the life cycles of stars in the early universe. Their presence in the Dragon Arc challenges prior assumptions and encourages astronomers to revisit models of galaxy formation and stellar development during this epoch.
Moreover, the discovery underlines the importance of gravitational lensing as a tool in modern astronomy. Initially predicted by Albert Einstein’s general theory of relativity, gravitational lensing occurs when massive objects like galaxy clusters bend the path of light traveling from distant sources. This bending can amplify light from faraway stars by factors of hundreds or thousands, effectively turning the cluster into a cosmic magnifying glass. Though previous studies have leveraged this effect to detect one or two stars in distant galaxies, the ability to resolve dozens of stars within a single galaxy has immense potential for statistical and comparative studies of stellar populations.
Lead author Yoshinobu Fudamoto, an assistant professor at Chiba University in Japan, emphasized the challenge posed by distant galaxies, which often appear as diffuse and indistinct blobs when observed through conventional telescopes. These “blobs” actually contain vast numbers of individual stars, the majority of which were previously indistinguishable. JWST, with its unparalleled light-collecting power, has turned this challenge into an opportunity by enabling scientists to isolate and study individual stellar points even in the universe’s most remote regions.
This breakthrough also offers tantalizing possibilities for probing dark matter—the invisible substance that constitutes approximately 27% of the universe’s mass-energy content but remains poorly understood. By studying how the gravitational fields of lensing clusters like Abell 370 influence the light from individual stars, astronomers can infer the distribution and properties of dark matter within these clusters. Observing more stars provides a richer dataset, enabling more precise investigations of dark matter’s elusive characteristics.
The significance of this work lies not only in the immediate findings but also in its potential to guide future research. As JWST continues to survey the Dragon Arc and other lensing galaxies, astronomers anticipate discovering hundreds of individual stars at similar distances. These observations will contribute to a more comprehensive understanding of stellar evolution, galaxy formation, and the interplay of baryonic and dark matter in shaping the cosmos.
The excitement surrounding this discovery also stems from the opportunities it provides for comparative studies. Astronomers have an extensive catalog of red supergiants in nearby galaxies like the Milky Way and Andromeda, where individual stars can be observed with relative ease. Applying this knowledge to red supergiants in galaxies billions of light-years away offers a unique perspective on how these stars evolved under the conditions of the early universe. Understanding the similarities and differences between these two populations could yield valuable insights into the processes driving stellar and galactic evolution.
Looking ahead, the integration of JWST’s capabilities with other cutting-edge tools in astronomy, such as the upcoming Extremely Large Telescope (ELT) and advanced spectroscopic instruments, promises an era of unprecedented discovery. Together, these technologies will allow scientists to delve deeper into the mysteries of distant stars and galaxies, bringing us closer to answering fundamental questions about the origins and dynamics of the universe.
Ultimately, the story of this discovery is a testament to human ingenuity, collaboration, and curiosity. It underscores our relentless pursuit of knowledge and the extraordinary potential of modern science to uncover the hidden wonders of the cosmos. Through a combination of natural cosmic phenomena and technological breakthroughs, astronomers have not only expanded the limits of observational astronomy but also opened new pathways to understanding our place in the universe.
Reference: Yoshinobu Fudamoto et al, Identification of more than 40 gravitationally magnified stars in a galaxy at redshift 0.725, Nature Astronomy (2025). DOI: 10.1038/s41550-024-02432-3