XRISM Finds Sulfur Between Stars: NASA & Japan Discovery
Sulfur Found in Solid Form in Interstellar Space, Revealing Clues to Star and Planet Formation
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For decades, scientists have detected sulfur gas drifting between stars. But what happens to this crucial element in the dense, cold regions where stars and planets are born has remained a mystery. Now, using the advanced capabilities of the XRISM spacecraft, researchers have, for the first time, directly observed sulfur existing as a solid within the interstellar medium, offering vital insights into the building blocks of planetary systems.
Unveiling Solid Sulfur in the Cosmos
Led by Lía Corrales, assistant professor of astronomy at the University of michigan in Ann Arbor, the research team pinpointed both gaseous and solid sulfur using XRISM’s high-resolution X-ray spectroscopy. Their findings, published June 27 in the Publications of the Astronomical Society of Japan, represent a significant leap forward in understanding the chemical composition of interstellar space.”Sulfur can easily change from a gas to a solid and back again,” explains Corrales. “The XRISM spacecraft provides the resolution and sensitivity we need to find it in both forms and learn more about where it might be hiding.”
Previously,scientists hypothesized that sulfur gas in dense interstellar clouds would condense into solids,potentially combining with ice or other elements. However, directly observing this process proved elusive – until now.
How XRISM Detected Interstellar Sulfur
The team employed a technique analogous to medical X-rays. Just as X-rays reveal bone structure by differential absorption, the researchers used a bright X-ray source – a binary star system named GX 340+0, located over 35,000 light-years away in Scorpius - to probe a specific region of the interstellar medium. By analyzing how the X-rays from GX 340+0 where altered as they passed through the medium, they could identify the presence and state of sulfur.
“We picked a portion of the interstellar medium with the right density – not so thin that all the X-rays would pass through unchanged, but also not so dense that they would all be absorbed,” Corrales explains.
The Resolve instrument on XRISM measured the energy of the X-rays, revealing that sulfur wasn’t just present as a gas, but also in solid form, potentially mixed with iron. This finding was further corroborated by observations of a second X-ray binary, 4U 1630-472.
Iron-Sulfur Compounds: A Cosmic Connection
The team’s analysis suggests the solid sulfur is likely bound with iron, forming compounds like pyrrhotite, troilite, and even pyrite (fool’s gold). This finding is particularly intriguing becuase iron-sulfur compounds are commonly found in meteorites.
“Chemistry in environments like the interstellar medium is very different from anything we can do on earth, but we modeled sulfur combined with iron, and it seems to match what we’re seeing with XRISM,” says Elisa Costantini, a senior astronomer at the Space Research Organization Netherlands and the University of Amsterdam. “Our lab has created models for different elements to compare with astronomical data for years. the campaign is ongoing, and soon we’ll have new sulfur measurements to compare with the XRISM data to learn even more.”
This suggests that iron-sulfur compounds could be a key mechanism for sulfur to solidify within molecular clouds and subsequently be incorporated into forming planets. The presence of these compounds provides a potential link between the raw materials of star formation and the composition of planetary bodies.
XRISM’s Breakthrough and Future Exploration
While NASA’s Chandra X-ray Observatory has previously studied sulfur, XRISM’s measurements are the most detailed to date. Brian Williams, the XRISM project scientist at NASA’s Goddard Space Flight Center, emphasizes the importance of this advancement.
“Since GX 340+0 is on the other side of the galaxy from us, XRISM’s X-ray observations are a unique probe of sulfur in a large section of the Milky Way. There’s still so much to learn about the galaxy we call home.”
the XRISM mission, a collaborative effort between JAXA (japan Aerospace Exploration Agency), NASA, and ESA (European Space Agency), is poised to continue unraveling the mysteries of the interstellar medium. The advancement of Resolve, the mission’s microcalorimeter spectrometer, by NASA and JAXA, has been instrumental in this breakthrough.Future observations promise to further refine our understanding of sulfur’s role in the cosmic cycle of star and planet formation, offering a deeper glimpse into the origins of our universe and potentially, life itself.