An international team of researchers with the help of the Japanese XRISM mission (X-ray Imaging and Spectroscopy Mission) conducted the first direct measurement of sulfur in gaseous and solid forms in the interstellar medium - a mixture of dust and gas between stars. Using data from X-ray observations of two distant binary systems, scientists traced the phase transitions of sulfur, which opens up new perspectives for understanding its cosmic distribution.
Details of the study
The results, published in the journal Publications of the Astronomical Society of Japan, are based on observations of the GX binary system 340+0 in the constellation Scorpio, located at a distance of over 35 000 light years. XRISM, thanks to the unique resolution of the Resolve tool, made it possible to detect sulfur as a gas, and in the solid state, probably, in compounds with iron. The study confirmed, that in dense interstellar regions sulfur disappears from the gas phase, condensing into solid forms, such as ice or minerals.
For additional verification, the team used data from another system, 4U 1630-472, which confirmed the presence of sulfur compounds, such as pyrrhotite, troilite and pyrite, which are often found in meteorites. These minerals match the XRISM spectral data, indicating their association with interstellar dust.
The value of sulfur in space
Leah Corrales, lead author of the study from the University of Michigan, noted, that sulfur plays an important role in biological processes on Earth, but its distribution in space remains a mystery. XRISM allows you to monitor its phase transitions, which helps to understand, where it can accumulate. Sulfur easily changes from a gas to a solid state and back again, which complicates its study in the interstellar medium, where the conditions are radically different from those on Earth.
Elise Costantini of the Netherlands Space Agency added, that laboratory models of sulfur compounds with iron agree with XRISM data, and further experiments will help clarify these observations. Brian Williams, XRISM project scientist at NASA's Goddard Space Flight Center, emphasized, that previous studies of sulfur were carried out using the Chandra observatory, but XRISM provides the most detailed measurements, allowing a large part of the Milky Way to be explored.
Technical aspects of the XRISM mission
Neglected 7 September 2023 year by the Japan Aerospace Exploration Agency (JAXA) in collaboration with NASA and ESA, XRISM is equipped with the Resolve X-ray spectrometer and the Xtend camera for wide-angle observation. The Resolve instrument provides unprecedented resolution in the 0.3–12 keV range, which allows analyzing the chemical composition of the interstellar medium. Observations of GX 340+0 used this system as a source of background X-ray radiation, which made it possible to study the absorption of sulfur in the interstellar medium on the way to Earth.
Meaning for science
The study of sulfur is not only important for astrochemistry, but also for understanding the evolution of galaxies. Sulfur, as one of the most common elements in the universe, is key to the formation of molecules in the interstellar medium, which affects the processes of star formation and the chemical composition of the planets. XRISM data will help refine models of interstellar dust and its interaction with gas, and will also answer the question about the distribution of heavy elements in the Milky Way.
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