Using data from the NASA/ESA/CSA James Webb Space Telescope, astronomers found that IRS 3 — a giant, bulging star orbiting just 0.55 light-years from Sagittarius A*, the Milky Way’s central black hole — is still forming silicate dust and harboring water molecules despite the galaxy’s most extreme radiation environment.
Mid-infrared image of the IRS 3 environment, observed using VLT/NACO and Webb/MIRI/MRS. Image credit: Bisker et al., doi: 10.1051/0004-6361/202660243.
At the heart of the Milky Way, Sagittarius A* dominates a violent neighborhood of intense radiation, strong winds and gravitational pressure.
Astronomers have long wondered how fragile particles and dust grains — the raw material for planets and ultimately life — can survive in such close proximity to such an environment.
“Galactic centers are among the most extreme environments, so understanding whether stars can continue to enrich their surroundings is an important question,” said Dr. Florian Biesecker, an astronomer at the University of Cologne.
“With Webb, we can directly observe how stars behave under these conditions and see that dust production remains remarkably resilient.”
IRS 3 is a red giant that is about 72 million years old and has a mass about 6 times that of the Sun.
The star is nearing the end of its life, spewing out layers of gas and dust in a phase astronomers call the giant asymptotic branch.
Using Webb’s MIRI instrument (Mid-Infrared Instrument), Dr. Peißker and his colleagues have produced the most complete infrared spectrum of the star ever, answering a long-standing question about the star’s chemistry.
Previous ground-based observations have left open the possibility that IRS 3 may be carbon-rich, but Webb’s new data show two telltale absorption features that are produced only by oxygen-rich, silicate-based dust.
This combination rules out a carbon-dominated composition and the IRS 3 is firmly classified as an oxygen-rich giant.
Perhaps most surprising is that astronomers have discovered clear signs of water molecules in the material surrounding the star.
Water and other complex molecules are extremely fragile, and can be easily broken apart by ultraviolet radiation and X-rays of the type that stream from the region around the black hole.
The finding of intact water so close to the galactic center suggests that the star’s dusty atmosphere is thick enough to protect sensitive chemistry from its harsh surroundings.
“This discovery was made possible by Webb’s high-power infrared instruments,” said Dr. Macarena Garcia-Marin, an astronomer at ESA.
“This is the first time a continuous mid-infrared spectrum has been collected for this star, allowing us to detect features of silicate dust and reveal the star’s true chemical identity.”
To interpret the spectrum, the researchers built computer models of the gaseous atmosphere and dust surrounding the star using radiation transfer code called Hyperion, testing nearly 100,000 variations before settling on the best fit.
Models point to a star about 60,000 times the luminosity of the Sun, and an envelope organized into several concentric shells, each with different temperatures, densities and dust compositions – hot aluminum oxide near the star giving way to cooling silicate grains farther away, with the temperature falling by about 1,000 K across the structure.
“The discovery of water is particularly exciting because it shows that molecular materials can survive in an environment dominated by intense radiation,” says Dr. Macarena.
“This tells us that even close to a supermassive black hole, stars can continue to contribute material back into their surroundings.”
the results Appear in the magazine Astronomy and astrophysics.
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F. Biesecker et al. 2026. Dust production in the extreme environment of Sagittarius A*. MIRI/JWST observation of the O-rich asymptotic giant star IRS 3. A&A 712, A79; Two: 10.1051/0004-6361/202660243
