XRISM Uncovers Sulfur in Gas and Solid States

XRISM's high resolution X-ray data reveal sulfur exists in both gaseous and solid forms in the Milky Way's interstellar medium, confirmed by observations of two X-ray binaries.

XRISM Maps Sulfur in Gas and Solid States Across the Galaxy

A study published on June 27, 2025, in the Publications of the Astronomical Society of Japan reports the first direct detection of sulfur in both gaseous and solid forms in the interstellar medium. Using XRISM's Resolve instrument, researchers analyzed X-ray emissions from two distant binary systems GX 340+0 and 4U 1630-472 to detect sulfur as it interacts with high energy photons. The findings point to sulfur existing in solid minerals, likely iron sulfides such as pyrrhotite, troilite, or pyrite, bound to dust grains.

The discovery broadens how scientists map the galaxy's chemistry. It shows sulfur can move between gas and solid states as material condenses in dense clouds and during planet formation. Scientists plan more observations and lab modeling to identify additional compounds and better match future data.

The finding shows XRISM can read chemical states in space as clearly as a medical scan reads tissues. It turns sulfur from a theoretical clue into a measurable part of the interstellar medium, offering a new way to test models of dust formation and the ingredients for planets. The result also highlights how quickly space science can move when new instruments unlock previously hidden details.

Yet the study also points to limits. Interpreting solid sulfur from X-ray absorption requires careful lab work to identify exact minerals. Researchers will need to map sulfur across more regions and combine X-ray data with ultraviolet and infrared observations to build a fuller picture of the galaxy’s chemical pathways.

Highlights

The universe keeps its chemical inventory close and new instruments may reveal more secrets.