Stunning galaxy cluster: Webb’s Picture of the Month
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ESA originally published this story on January 22, 2026. Edits by EarthSky.
A galaxy cluster and its lensed galaxies
Check out the beautiful image above from the James Webb Space Telescope. Most of the specks you see pictured there are distant galaxies. First, notice the galaxy cluster MACS J1149.5+2223, or MACS J1149 for short. At the cluster’s center is a huddle of elliptical galaxies that appears ghostly in this image, yet rules over the cluster with immense gravity.
MACS J1149 is some 5 billion light-years away in the direction of the constellation Leo the Lion. Astronomers have confirmed more than 300 galaxies belonging to this great cluster and have identified several hundred more possible members. The combined mass of all these galaxies gives the cluster colossal self-gravity. That gravity holds the member galaxies together as they drift through space.
Now look again. See the faint curved arcs in the image, and the strangely distorted shapes of some of the galaxies? MACS J1149 is so massive – and its gravity so powerful – that it bends the light of other galaxies not bound to the cluster, but located far, far behind it. In the image above, the curved arcs are distant background galaxies whose light has been magnified and distorted by gravitational lensing from the massive foreground cluster.
Notice the ‘pink jellyfish’
This phenomenon of gravitational lensing lets us see distant galaxies we wouldn’t be able to see otherwise. That’s what you’re seeing scattered across the image of MACS J1149: subtle and not-so-subtle examples of gravitational lensing, from galaxies that appear to have been stretched into narrow streaks of light to galaxy images that have morphed into strange shapes.
You can see a fantastic example of gravitational lensing near the center of the image. Look just below the brilliant white galaxies at the heart of the cluster. There, the image of a galaxy with distinct spiral arms has morphed into something resembling a pink jellyfish. This tangled-looking galaxy is home to what was once the most distant single star ever discovered as well as a supernova whose image appeared four times at once.
Pan through the spectacular galaxy cluster in this video from ESA.
A celebrity galaxy cluster
MACS J1149 has long received the celebrity treatment from leading telescopes, and for good reason. This cluster was one of six investigated through the Hubble Space Telescope’s Frontier Fields program. Scientists selected the Frontier Fields galaxy clusters for the strength of their gravitational lensing. Their ability to warp spacetime has granted researchers a glimpse into the early universe.
Now, Webb is pushing our knowledge horizon to even earlier times, enabling new discoveries like a feasting supermassive black hole less than 600 million years after the Big Bang. Using Webb’s Near-Infrared Spectrograph (NIRSpec), Near-InfraRed Camera (NIRCam), and Near-InfraRed Imager and Slitless Spectrograph (NIRISS), researchers are revealing never-before-seen details of the lives of early galaxies.
Scientists collected the Webb data for this image as part of the Canadian NIRISS Unbiased Cluster Survey (CANUCS) program #1208 (PI: C. J. Willott). This program uses Webb’s sensitive instruments to unveil the evolution of low-mass galaxies in the early universe, revealing their star formation, dust and chemistry. The data will also help researchers study the epoch of reionization, when the first stars and galaxies lit up the universe, map the distribution of mass within galaxy clusters, and understand how star formation can slow to a trickle in a cluster environment.
Bottom line: The Webb space telescope has imaged the stunning galaxy cluster MACS J1149, putting a spotlight on its prominent gravitational lensing.
Read more: A fast-growing supermassive black hole in the early universe
The post Stunning galaxy cluster: Webb’s Picture of the Month first appeared on EarthSky.