Pandora’s Cluster Mapped by UNCOVER

Hidden within the heart of the massive galaxy cluster Abell 2744, also called Pandora’s Cluster, are tiny green galaxies that may have helped transform the early universe. Located about 4 billion light-years away in the constellation Sculptor, this colossal cluster acts as a natural gravitational lens, magnifying far more distant galaxies behind it and extending Webb’s reach into the cosmic past.

The image, taken as part of the UNCOVER (Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization) program, reveals galaxies that existed when the universe was less than a billion years old. These small, compact systems appear green in Webb’s filters because of light emitted by doubly ionized oxygen, which is evidence of intense starburst activity.

During that early epoch, the universe’s hydrogen gas shifted from neutral to ionized, clearing the cosmic fog and making starlight visible across space. Scientists suspect that galaxies like these, rich in new stars and ultraviolet light, may have driven that transformation. Webb’s discovery of them marks an essential step toward understanding how the first galaxies reshaped the universe.