Webb: a collision favoured to explain GS18660’s ring
· BehindLines newsroom
A ring of forming stars surrounds the centre of GS18660, a galaxy observed with the James Webb Space Telescope. The study published on 8 September 2026 in Astronomy & Astrophysics describes it at a time when the Universe was only about two billion years old. Interaction with a small neighbouring galaxy is the favoured explanation; the possible role of a bar remains to be clarified. Published study.
The data do not come from an observation carried out this autumn. The preprint records an acquisition on 26 November 2024 with NIRSpec, Webb’s spectroscopic instrument; it was submitted in December 2025. This chronology separates data collection, the first release of the work and its publication in a journal. Initial version and method.
NIRSpec allows light to be examined at different points across the system. The researchers can thus connect the visible structure, gas motions and the history of star formation. They find a rotating disc with additional motions that are difficult to explain by rotation alone. Their modelling yields a radial component of around 200 kilometres per second. Its exact amplitude and interpretation nevertheless remain uncertain.
A companion galaxy lies nearby. Its velocity offset relative to GS18660, measured spectroscopically along our line of sight, reaches about 425 kilometres per second. Together with structures linking the two objects and the presence of young stars in the ring, this combination of clues favours a recent interaction. It is not a direct observation of the collision.
The authors nevertheless retain another possibility: a bar structure could help organise the gas and produce a ring through resonance. An interaction could also have triggered a bar, followed by the ring, so the scenarios do not necessarily exclude one another. Deeper images, particularly with NIRCam, would help distinguish the stellar populations and clarify the nature of this structure.
The system’s interest therefore lies as much in this uncertainty as in its shape. Distinguishing between the mechanisms would shed light on how galaxies organised themselves in the young Universe. Further observations will allow researchers to test whether the signatures brought together today are sufficient to explain its formation.