ALMA uncovers sulfur for the first time around a rare class of supergiant star

Astronomers have discovered sulfur-bearing molecules surrounding the rare massive star HD 87643, marking the first detection of sulfur chemistry around a B[e] supergiant. The study, published in The Astrophysical Journal Letters, found emissions from 10 different sulfur-bearing molecules, including SO, SO2, and 13CS. These findings expand the molecular inventory of HD 87643, previously limited to CO. The research, led by Cristobal Bordiu of INAF Catania Astrophysical Observatory, used the Atacama Large Millimeter/submillimeter Array to conduct the first detailed millimeter-wavelength survey of this extreme B[e] supergiant.

The study reveals that sulfur chemistry around B[e] supergiants has remained largely unexplored, with only one sulfur-bearing molecule previously detected. The ratio of two isotopes of sulfur monoxide is significantly lower than expected, suggesting that the rarer, heavier isotope is more prevalent near the star. This phenomenon, known as mass-independent fractionation, has been observed in ancient rock samples and meteorites but is rare in stellar environments. The researchers propose that the star's intense ultraviolet light breaks apart sulfur dioxide molecules, converting them into sulfur monoxide, but the process is not uniform across isotopes.

This discovery provides new insights into the chemical evolution of massive stars and the distribution of elements necessary for life. It highlights the importance of studying sulfur chemistry in extreme stellar environments, as such processes may play a role in the formation of planets and the emergence of life. Future high-resolution ALMA observations could help refine the understanding of this star's sulfur chemistry.

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