Gravitational Arcs in 'El Gordo' Galaxy Cluster | James Webb Space Telescope
Webb’s infrared image of the galaxy cluster El Gordo (“the Fat One”) reveals hundreds of galaxies, some never before seen at this level of detail. El Gordo acts as a gravitational lens, distorting and magnifying the light from distant background galaxies. Two of the most prominent features in the image include the Thin One, highlighted in box A, and the Fishhook, a red swoosh highlighted in box B. Both are lensed background galaxies. The insets at right show zoomed-in views of both objects.
A new image of the galaxy cluster known as “El Gordo” is revealing distant and dusty objects never seen before, and providing a bounty of fresh science. The infrared image, taken by NASA’s James Webb Space Telescope, displays a variety of unusual, distorted background galaxies that were only hinted at in previous Hubble Space Telescope images.
El Gordo is a cluster of hundreds of galaxies that existed when the universe was 6.2 billion years old, making it a “cosmic teenager.” It is the most massive cluster known to exist at that time. (“El Gordo” is Spanish for the “Fat One.”)
The team targeted El Gordo because it acts as a natural, cosmic magnifying glass through a phenomenon known as gravitational lensing. Its powerful gravity bends and distorts the light of objects lying behind it, much like an eyeglass lens.
The Fishhook
Within the image of El Gordo, one of the most striking features is a bright arc represented in red at upper right. Nicknamed “El Anzuelo” (The Fishhook) by one of Frye’s students, the light from this galaxy took 10.6 billion years to reach Earth. Its distinctive red color is due to a combination of reddening from dust within the galaxy itself and cosmological redshift due to its extreme distance.
By correcting for the distortions created by lensing, the team was able to determine that the background galaxy is disk-shaped but only 26,000 light-years in diameter—about one-fourth the size of the Milky Way. They also were able to study the galaxy’s star formation history, finding that star formation was already rapidly declining in the galaxy’s center, a process known as quenching.
The Thin One
Another prominent feature in the Webb image is a long, pencil-thin line at left of center. Known as “La Flaca” (the Thin One), it is another lensed background galaxy whose light also took nearly 11 billion years to reach Earth.
Not far from La Flaca is another lensed galaxy. When the researchers examined that galaxy closely, they found three images of a single red giant star that they nicknamed Quyllur, which is the Quechua term for star.
Quyllur is the first individual red giant star observed beyond 1 billion light-years from Earth. Such stars at high redshift are only detectable using the infrared filters and sensitivity of Webb.
“Gravitational lensing was predicted by Albert Einstein more than 100 years ago. In the El Gordo cluster, we see the power of gravitational lensing in action,” concluded Rogier Windhorst of Arizona State University, principal investigator of the PEARLS program. “The PEARLS images of El Gordo are out-of-this-world beautiful. And, they have shown us how Webb can unlock Einstein's treasure chest.”
Brenda Frye of the University of Arizona is co-lead of the PEARLS-Clusters branch of the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) team. A related paper by Frye et al. has been published in the Astrophysical Journal:
https://iopscience.iop.org/article/10.3847/1538-4357/acd929/pdf
Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Image Credits: NASA, European Space Agency/Canadian Space Agency
Science: Jose M. Diego (IFCA), Brenda Frye (University of Arizona), Patrick Kamieneski (ASU), Tim Carleton (ASU), Rogier Windhorst (ASU)
Image Processing: Alyssa Pagan (STScI), Jake Summers (ASU), Jordan C. J. D'Silva (UWA), Anton M. Koekemoer (STScI), Aaron Robotham (UWA), Rogier Windhorst (ASU)
Release Date: Aug. 2, 2023
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