Saturday, June 14, 2025

Webb Sees the Galaxies that Cleared Out the Cosmic Fog

White diamonds show the locations of 20 of the 83 young, low-mass, starburst galaxies found in infrared images of the giant galaxy cluster Abell 2744. This composite incorporates images taken through three NIRCam filters (F200W as blue, F410M as green, and F444W as red). The F410M filter is highly sensitive to light emitted by doubly ionized oxygen — oxygen atoms that have been stripped of two electrons — at a time when reionization was well underway. Emitted as green light, the glow was stretched into the infrared as it traversed the expanding universe over billions of years. The cluster’s mass acts as a natural magnifying glass, allowing astronomers to see these tiny galaxies as they were when the universe was about 800 million years old. NASA/ESA/CSA/Bezanson et al. 2024 and Wold et al. 2025

The early universe was shrouded in darkness. Just hundreds of millions of years after the Big Bang, a thick fog of hydrogen gas choked the cosmos, blocking light from traveling far. At some point, this gas became ionized, stripped of its electrons. Thanks to the James Webb Space Telescope, astronomers have identified the culprit: low-mass starburst galaxies emitting huge amounts of ultraviolet light. In just one patch of sky. They discovered 83 of these galactic powerhouses in one part of the sky at a time when the Universe was only 800 million years old.



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