天文学：南のリング星雲の形成を明らかにする

At least four stars were responsible for creating the ring shape and the detailed filamentary structures of the Southern Ring Nebula, a paper published in Nature Astronomy this week proposes. The findings are based on an analysis of data from the James Webb Space Telescope (JWST).

Planetary nebulae are created when stars similar in mass to our Sun develop, cool down, and shed their outer layers of material, which gradually expand outwards. Further stellar evolution creates an ultra-hot white dwarf star, which then begins to illuminate the cast-off material from the star’s earlier life. Within the Southern Ring Nebula (NGC 3132), the white dwarf and a visual companion can be seen close to the centre of the ring structure.

To explore the Southern Ring Nebula in greater detail, Orsola De Marco and colleagues analysed data from JWST’s Near-Infrared Camera and Mid-Infrared Instrument, and by modelling several observed characteristics of the central stars and the nebula, found that the two stars cannot have shaped the nebula by themselves. When the authors analysed the very centre of the nebula they found evidence of at least two stars hidden within a dusty disk — the white dwarf and one other previously unknown star — which primarily would have shaped the nebula. Arc-like features imaged for the first time by JWST in the outer nebula imply that another star orbits close to the inner two, although it too is not directly seen.

The authors suggest these findings indicate that the stellar system that led to the Southern Ring Nebula contained at least four stars. They suggest further JWST data will aid our general understanding of the astrophysical processes that lead to the formation of planetary nebulae.