68 galaxies containing green seeds
JWST images of the full sample of 68 hydrogen-alpha emitters that contain green seeds. [Chen et al. 2025]
The peak of cosmic star formation, also called cosmic noon, took place when the universe was 2–3 billion years old. During this time, roughly half of the stellar mass present in galaxies today was formed, and the structures that existed during cosmic noon provide important clues to how galaxies evolved to their current forms. Recently, Nuo Chen (The University of Tokyo and National Astronomical Observatory of Japan) and collaborators used JWST to look back to cosmic noon and study hydrogen-alpha emitters — galaxies with prominent hydrogen-alpha emission, signaling active star formation. Within these star-forming galaxies, Chen’s team discovered compact regions of bright green emission, which they named green seeds. The images above and to the right show 68 hydrogen-alpha emitters hosting a total of 128 green seeds. The team also found 59 red seeds, which are similarly compact regions that are redder in color, indicating an older or dustier population of stars. Green seeds appear to be sites of intense star formation that has been triggered either by galaxy mergers or gravitational instabilities. What these green seeds evolve into is still unknown, but Chen and collaborators suspect that massive green seeds might migrate to the centers of their galaxies, morph into red seeds, and eventually form the central bulges of their galaxies. On the other hand, low-mass green seeds might dissipate over time. To learn more about green seeds and galaxies at cosmic noon, be sure to check out the full research article linked below.
Citation
“Compact [O iii] Emission-line Regions (“Green Seeds”) in Hα Emitters at Cosmic Noon from JWST Observations,” Nuo Chen et al 2025 ApJ 981 96. doi:10.3847/1538-4357/adad69