Astronomers using the James Webb Space Telescope (IWST) have captured the first images of individual stars from the Dragon Arc galaxy over 6.5 billion light years away using the bending of light caused by the massive gravity of the Abel 370 galaxy cluster.
Known as gravitational lensing, the process uses the light-bending power of gravity to focus the JWST’s instruments on objects too far away to image directly. A similar process using the lenses in a telescope or binoculars allows the human eye to see beyond its normal range.
“To us, galaxies that are very far away usually look like a diffuse, fuzzy blob,” said the lead author of the study outlining the discovery, Yoshinobu Fudamoto, an assistant professor at Chiba University in Japan and a visiting scholar at Steward Observatory. “But actually, those blobs consist of many, many individual stars. We just can’t resolve them with our telescopes.”
The researchers behind the discovery hope to use this method to search for more distant stars captured by the JWST. They also believe their work could help resolve the longstanding mystery of dark matter.
Gravitational Lensing Caused by Dragon Arc Predicted by Einstein
Decades before humanity launched its first observatories into space, famed 20th-century scientist Albert Einstein suggested that human-made telescopes could take advantage of gravitational lensing if the object being viewed was in line with a large source of gravity from Earth’s point of view. If the gravitational source was strong enough, Einstein predicted that gravitational lensing could amplify distant light by a factor of hundreds or even thousands.
More recently, astronomers have started to use gravitational lensing to observe stars and other cosmic structures that are too far away to image directly. Still, the process has its limitations. According to Fudamoto, most successful gravitational lensing observations have been limited in scope.
“These findings have typically been limited to just one or two stars per galaxy,” the professor explained. “To study stellar populations in a statistically meaningful way, we need many more observations of individual stars.”
In their recent work, Fudamoto and colleagues report the successful imaging of several stars at once thanks to a combination of microlensing caused by galaxies and microlensing caused by individual stars.
Researchers “Stumbled” Upon Discovery When Studying JWST Images
While the imaging of individual stars 6.5 billion light years from Earth is unprecedented, the researchers found them by chance. According to Fengwu Sun, a former U of A graduate student who is now a postdoctoral scholar at the Center for Astrophysics | Harvard & Smithsonian, he was studying images of the Dragon Arc captured by the JWST when he “stumbled upon a treasure trove” of individual stars.
The discovery was possible because the Dragon Arc galaxy is located in line with a galaxy cluster roughly 4 billion light years away from Earth, Abel 370. According to the researchers, the massive gravitational pull of Abel 370 bends the light from Dragon Arc into an elongated shape, “like a hall of mirrors of cosmic proportions.”
When the team examined the images the JWST captured in December 2022 and 2023, they spotted 44 stars that should have been too far away to see. They also noticed that the brightness of the distant stars fluctuated with the galaxy cluster’s gravitational lensing landscape, confirming that they were from the Dragon Arc.
Astronomers Thank Their “Lucky Stars’ for Discovery
In the study’s conclusion, the researchers point out that imaging stars this far away involved the gravitational lensing from Abel 370 and another effect they are calling “lucky stars.” Specifically, the team says that the powerful macro-lending effect of Abel 370 was combined with a micro-lensing effect of individual stars that happened to be in perfect alignment to be captured by the JWST.
“Inside the galaxy cluster, there are many stars floating around that are not bound by any galaxy,” said co-author Eiichi Egami, a research professor at Steward Observatory. “When one of them happens to pass in front of the background star in the distant galaxy along the line of sight with Earth, it acts as a microlens, in addition to the macro lensing effect of the galaxy cluster as a whole.”
According to Fudamoto, astronomers observing the same galaxy several times can watch as this alignment appears and disappears. This change, which can take place over a few days, causes stars in distant galaxies too far away to image directly to “appear to pop in and out of existence.”
“This is a result of the varying effective magnifications from the macro- and microlensing effect as the microlensing stars move in and out of the line of sight,” the professor explained.
Next, the researchers hope to study additional images of distant galaxies captured by the JWST to capture even more individual stars within the Dragon Arc galaxy. If successful, the team says their efforts could lead to detailed studies of distant stars and galaxies previously unavailable to astronomers. The team also believes their work can help shed some light on the elusive dark matter that makes up around 85% of the universe.
“This groundbreaking discovery demonstrates, for the first time, that studying large numbers of individual stars in a distant galaxy is possible,” Sun said, “as long as nature is there to lend a helping hand.”
The study “Identification of more than 40 gravitationally magnified stars in a galaxy at redshift 0.725” was published in Nature Astronomy.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.