A galaxy nicknamed Misty Moons offers a glimpse of early star formation

A galaxy nicknamed Misty Moons, located at a redshift of roughly 11 to 12, was identified by astronomers using gravitational lensing effects from a massive galaxy cluster. The galaxy, which existed when the universe was less than 500 million years old, is magnified by the cluster's gravity, allowing researchers to reconstruct its internal structure. The team used JWST's NIRCam images of the MACS J0257.1-2325 cluster field, complemented by older Hubble images, to detect the galaxy. The galaxy appears as two blobs, ID1 and ID2, and is strongly magnified, with two of its bright lensed images 20 to 30 times brighter than they would be without magnification. The study reveals four clumps in ID1 and three in ID2, each containing about 10 million solar masses of young, dust-poor stars, around 40 to 70 million years old.

• The clumps resemble local nuclear star clusters and young massive clusters and may be proto-globular clusters.
• Together, these clumps account for at least 80% of the galaxy's stellar mass.
• The galaxy's star formation density is 100 to 10,000 times higher than in local dwarfs, suggesting intense star formation in the early universe.

The discovery highlights the role of gravitational lensing in revealing the structure of early galaxies. The galaxy's high star formation density and clumpiness suggest that star formation in the early universe was concentrated in compact regions. The findings support the idea that high-redshift clumpy galaxies are distinct from local dwarf galaxies, not only in their high star formation surface densities but also in their short, bursty star formation during the early formation phase. The study also notes that the central clumps are bright and compact enough that the team cannot exclude a contribution from an actively feeding supermassive black hole. If present, some of the light, and so possibly some of the inferred star formation, could come from black hole accretion rather than stars.

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