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Groundbreaking Discovery Using James Webb Space Telescope Reveals Individual Stars in Distant Galaxy
Astronomers have always faced challenges when it comes to observing distant galaxies, akin to trying to discern tiny details on the moon with just binoculars. However, a significant breakthrough has been achieved by a research team led by the University of Arizona’s Steward Observatory, utilizing NASA’s James Webb Space Telescope (JWST) to identify individual stars in a galaxy located approximately 6.5 billion light-years from Earth, during a period when the universe was only half its current age.
This groundbreaking find, published in the journal Nature Astronomy, documents the largest collection of individual stars detected in the early universe. The researchers made this identification through the phenomenon known as gravitational lensing, combined with the advanced light-collecting ability of the JWST.
Typically, galaxies, including our own Milky Way, house billions of stars, and astronomers can observe these stars in closer galaxies like Andromeda. In contrast, stars in galaxies billions of light-years away appear as a blurred mass of light because their brightness diminishes over vast distances, complicating studies of galaxy formation and evolution.
“To us, galaxies that are very far away usually look like a diffuse, fuzzy blob,” explained Yoshinobu Fudamoto, an assistant professor at Chiba University and lead author of the study. “But those blobs are actually composed of countless individual stars that our telescopes struggle to resolve.”
Recent innovations in astronomy have harnessed the phenomenon of gravitational lensing, whereby massive objects distort the fabric of space-time and amplify the light from distant stars. This gravitational effect, first predicted by Albert Einstein, can enhance the brightness of distant stars, making them detectable by sensitive instruments like JWST.
Fudamoto noted the limitation in previous findings, which typically involved only one or two stars per galaxy. “To study stellar populations in a statistically significant way, we require observations of a larger number of individual stars,” he added.
Fengwu Sun, a former University of Arizona graduate student who is now a postdoctoral scholar at the Center for Astrophysics | Harvard & Smithsonian, serendipitously uncovered a wealth of individual stars while examining JWST images of a galaxy known as the Dragon Arc. This galaxy is situated behind the massive galaxy cluster Abell 370, which acts as a gravitational lens to stretch the image of the Dragon Arc into an elongated form.
In December 2022 and 2023, JWST captured two images of the Dragon Arc, in which astronomers identified 44 individual stars that exhibited variations in brightness over time due to the dynamic environment of the gravitational lensing.
“This remarkable discovery shows for the first time that we can study large numbers of individual stars in a distant galaxy,” Sun remarked, crediting the alignment of natural phenomena for this achievement.
However, it is important to note that even the substantial gravitational magnification from a galaxy cluster is insufficient to observe stars in galaxies that are even more distant. The success of this discovery hinged on a fortunate alignment of stars.
Eiichi Egami, a research professor at Steward Observatory and co-author of the study, provided insight into the mechanics. “Inside the galaxy cluster, there are many stars that are not gravitationally bound to any particular galaxy,” he explained. “When one of these stars aligns with a background star from the distant galaxy, it acts as a microlens, complementing the macrolensing effect of the galaxy cluster.”
The synergy of macrolensing and microlensing dramatically boosts the magnification factor, enabling JWST to detect individual stars that would otherwise remain too faint and distant to observe.
Interestingly, the stars within this magnifying cluster exhibit motion relative to the distant target stars and Earth. This shifting alignment alters the effective magnification over short periods—from mere days to weeks. When stars become optimally aligned, their brightness and apparent size increase significantly, only to wane again shortly thereafter.
“By repeatedly observing the same galaxy, we can identify stars that appear to flicker in and out of visibility,” Fudamoto said, referencing the variations caused by the dynamic microlensing conditions.
The research team analyzed the colors of the stars within the Dragon Arc and discerned a prevalence of red supergiants, akin to Betelgeuse, which are nearing the end of their life cycles. This observation stands in contrast to earlier studies that predominantly found blue supergiants, which are some of the brightest stars known. The ability of JWST to observe at infrared wavelengths allows for the detection of cooler stars, underscoring the telescope’s capabilities.
Future observations with JWST are anticipated to uncover even more magnified stars within the Dragon Arc galaxy, facilitating detailed studies of hundreds of stars in remote galaxies. These observations could enhance our understanding of the structures of gravitational lenses and provide clues about the elusive nature of dark matter.
This research was supported by multiple funding sources, including NASA and the National Science Foundation.
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