The powerful infrared eyes of the James Webb Space Telescope have notched another record for extremely long-range viewing.
Thanks to the $10 billion observatory with strong ties to Tucson, researchers from the University of Arizona and elsewhere managed to identify 44 stars across a once-impossible distance of almost 6.5 billion light-years. That’s the largest number of individual stars ever detected in the distant universe, though that record is not expected to stand for very long.
“This groundbreaking discovery demonstrates, for the first time, that studying large numbers of individual stars in a distant galaxy is possible,” said Fengwu Sun, a former U of A graduate student who is now a postdoctoral scholar at the Harvard and Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
A Hubble Space Telescope image of the Abell 370 galaxy cluster also includes the far-more-distant Dragon Arc galaxy, which appears as a drawn-out smear of light near the center of the image. A University of Arizona-led international research team has used higher-resolution images captured by the James Webb Space Telescope to identify 44 individual stars in the Dragon Arc.
An international team of 47 researchers — including Sun and led by astronomers from the University of Arizona’s Steward Observatory — published their findings Monday in the journal Nature Astronomy.
It was Sun who stumbled onto the collection of stars while inspecting Webb images of a galaxy known as the Dragon Arc from a time when the universe was only about half its current age.
Even with Webb’s powerful instruments, the Dragon Arc stars were only visible from such a distance thanks to gravitational lensing, a phenomenon predicted by Albert Einstein in which objects massive enough to bend the fabric of space can distort and amplify the light from even more distant stars and galaxies.
From Webb’s vantage point, the Dragon Arc is located behind a massive cluster of galaxies roughly 4 billion light-years from Earth called Abell 370, where an invisible halo of dark matter produces strong gravitational fields that act as a sort of cosmic magnifying glass.
Most galaxies contain tens of billions of stars, but picking out the light from individual stars is virtually impossible from billions of light-years away.
“To us, galaxies that are very far away usually look like a diffuse, fuzzy blob,” said the study’s lead author, Yoshinobu Fudamoto, a visiting scholar at Steward Observatory from Chiba University in Japan. “But actually, those blobs consist of many, many individual stars. We just can’t resolve them with our telescopes.”
In this case, though, multiple layers of gravitational lensing from Abell 370 managed to magnify a few dozen stars in the Dragon Arc just enough for Webb to pick them up using the most powerful infrared instruments ever deployed in space.
This graphic shows how the invisible halo of dark matter within a galaxy cluster 4 billion light-years from Earth works as a “macrolens,” while lone, unbound stars drifting through the cluster act as additional “microlenses,” multiplying the factor of magnification for another galaxy another 2.5 billion light-years away.
“Inside the galaxy cluster, there are many stars floating around that are not bound by any galaxy,” explained study 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 micro-lens, in addition to the macro-lensing effect of the galaxy cluster as a whole.”
Several dozen U of A astronomers, engineers and students helped in the development of Webb’s two main instruments: the Near Infrared Camera, or NIRCam, and the Mid-Infrared Instrument, or MIRI.
Regents’ professor Marcia Rieke led the development team and now serves as principal investigator for NIRCam, which operates using light sensors designed, built and tested at the U of A. Her husband, fellow Regents’ professor George Rieke, is science team lead for MIRI, a camera and spectrograph he helped design.
There’s also a Southern Arizona connection to gravitational lensing itself.
The phenomenon was purely theoretical until 1979, when it was observed for the first time by astronomers Dennis Walsh, Bob Carswell and Ray Weymann at Kitt Peak National Observatory. They used the 2.1-meter telescope there to determine that twin quasars in the constellation Ursa Major were actually a single quasar whose image had been split by gravitational lensing.
A wider view, captured by Hubble, of Abell 370, one of the first galaxy clusters in which astronomers observed the phenomenon of gravitational lensing. The cluster’s gravitational field warps spacetime and distorts the light from galaxies lying far behind it, which show up as arcs and streaks in the picture.
In the future, researchers expect to identify dozens or even hundreds more magnified stars in the Dragon Arc galaxy using the Webb Space Telescope.
In the process, they hope to learn more about the structure of gravitational lenses and probe the mysteries of dark matter.
At least some of that work will almost certainly originate from Tucson. As a result of the U of A’s outsized contribution to the space telescope, NASA has allotted 13% of Webb’s total observing time to the university, the most of any astronomy center in the world.
