The galaxy cluster Abell S1063 dominates the center of this JWST image. It's a massive cluster of galaxies about 4.5 billion light-years away. While it dominates the picture, it's not the primary target. It serves as a gravitational lens that magnifies even more distant galaxies that appear as glowing strings of light around its circular edges.
When the JWST became operational, it had a long list of observing targets. Many of its targets were already visited by the Hubble Space Telescope, and astronomers were eager to use the JWST to dig deeper into things and find answers to their questions. Abell S1063 and the distant galaxies it magnifies were among those targets.
The Hubble Frontier Fields Program was an observing effort that lasted from 2013 to 2017. Its targets were six galaxy clusters, including Abell S1063. Each cluster was observed for about 140 orbits, making the images some of the deepest ever acquired. The goal was to use each cluster as a gravitational lens to magnify galaxies that formed when the Universe was very young. Some of the background galaxies were magnified 100 times.
The Hubble worked with other telescopes like the Spitzer Space Telescope on the program, and the rich dataset led to many discoveries about the early Universe, dark matter, and how things played out in the Universe's first billion years.
Here's Hubble's image of Abell S1063. While impressive, a quick comparison to the JWST's image shows how much more powerful the JWST is.
This is the Hubble Space Telescope's image of Abell S1063. Image Credit: NASA, ESA, STScI, and the HFF team
Here are the images side by side for an easy comparison.
Nobody who loves space and astronomy will speak poorly of the Hubble and its massive contribution to our understanding of Nature. But the JWST is clearly a more powerful instrument, even if it's not yet as venerated as the HST. Image Credit: (L) NASA, ESA, STScI, and the HFF team. (R) ESA/Webb, NASA & CSA, H. Atek, M. Zamani (ESA/Webb)
In the new image, astronomers used the JWST's Near-Infrared Camera (NIRCam) to look back in time even further than the Hubble and fill its frame with even more ancient galaxies. It's a jewelry box collection of sparkling galactic gems, stretched into bracelets by Abell S1063's gargantuan mass and light-amplifying power.
Gravitational lenses don't have a single focal point like optical lenses. Instead, they have a focal line that appears as a ring. The light from distant galaxies is stretched into partial arcs around the ring, and the same galaxy can appear in multiple distorted images.
The JWST image is also a deep field. The telescope took nine separate snapshots of different near-infrared light wavelengths, adding up to 120 hours of telescope time. This is Webb's deepest look at a single object yet. The length of exposure time, combined with Abell S1063's ability to magnify light, reveals some of the Universe's first galaxies.
The distant galaxies magnified in the image are otherwise out of reach. Thanks to Abell S1063, astronomers can see some of their internal structures and even define different stellar groups. The amplified light even lets them obtain detailed spectra and determine metallicities, a critical objective of studying the ancient Universe, since metallicity has increased as the Universe ages.
When a lens produces multiple images of the same galaxy, the light takes a different path for each image. Sometimes, these images are from different epochs, allowing astronomers to observe how a galaxy has changed over time.
This image is a zoomed-in portion of the whole picture, showing some of the detail the Webb reveals. Image Credit: ESA/Webb, NASA & CSA, H. Atek, M. Zamani (ESA/Webb)
The JWST's images of Abell S1063 are part of the General Observing program 3293. It's called GLIMPSE: gravitational lensing & NIRCam imaging to probe early galaxy formation and sources of reionization.
GLIMPSE has several objectives, including probing the typical galaxy population during the Dark Ages.
"This unprecedented dataset will showcase the full potential of JWST," the GLIMPSE program description states.