High-resolution observations of star-forming regions reveal sulfur as both a gas and a solid in the interstellar medium—hinting at the composition of dust and the chemistry of the galaxy
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Subtitle: T
Tags: Charisma, XRISM, sulfur, interstellar medium, interstellar dust, cosmic dust, Milky Way Galaxy, X-ray spectroscopy, Resolve, GX 340+0, 4U 1630–472, PASJ, NASA, JAXA, astronomy
Key phrase: Sulfur in the interstellar medium
Synonyms: interstellar sulfur, sulfur in cosmic dust, sulfur depletion, iron-sulfur compounds, XRISM, X-ray spectroscopy, GX 340+0, 4U 1630–472
SLUG: xrism-interstellar-sulfur-milky-way
An international team of scientists has made a groundbreaking measurement of elemental sulfur scattered throughout space, using observations from the Japanese Charismatic satellite.
By analyzing X-rays emitted from two binary star systems, astronomers have detected sulfur in the interstellar medium – the mixture of gas and dust that fills the space between stars. This is the first time sulfur has been directly observed in both its gaseous and solid forms. The discovery was made possible by the XRISM satellite, which allows scientists to study the universe in extraordinary detail.
"Sulfur is important to how cells in our bodies function here in Israel, but we still have many questions about where it is in the universe," said Leah Corrales, senior lecturer in astronomy. "Sulfur can quickly change from a gas to a solid and back again. The Charisma satellite provides the resolution and sensitivity needed to find it in both forms and discover where it is hiding."
Where did the sulfur go?
Using UV light, the researchers found gaseous sulfur in the space between stars. In denser parts of the interstellar medium, such as the molecular clouds where stars and planets form, sulfur in this form quickly disappears.
Scientists assume that the sulfur condenses into a solid, by combining with ice or mixing with other elements.
When a doctor takes an X-ray here on Earth, he places the patient between an X-ray source and a detector. Bones and tissues absorb different amounts of the light as it passes through the patient's body, creating contrast in the detector.
Watch the CHRISTIMS satellite's unprecedented look at the sulfur in our galaxy.
To study sulfur, Corrales and her colleagues did something similar.
They chose a part of the interstellar medium with the right density – not too thin that all X-rays would pass through unchanged, but not too dense that they would all be absorbed.
The team then selected a source of bright X-ray radiation behind that part of the core, a binary star called GX 340+0 that is more than 35,000 light-years away in the southern constellation Scorpius.
Using the Resolve instrument on the Cresset, scientists were able to measure the energy of GX 340+0's X-rays and determined that the sulfur exists not only as a gas, but also as a solid, perhaps mixed with iron.
"The chemistry in environments like the interstellar medium is different than what we can do here, but we modeled sulfur with iron, and it seems to match what we saw using CHRISMA," said co-author Alisa Constantini. "Our lab has created models of different elements to compare with many years of astronomical data. The work is ongoing and we will soon have new sulfur measurements to compare with CHRISMA data to advance our knowledge."
Iron-sulfur compounds are common in meteorites, so scientists have long thought this was one way sulfur solidifies from molecular clouds to travel through the universe.
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