Using data from the NASA/ESA/CSA James Webb Space Telescope, astronomers have discovered that IRS 3, a swollen giant star orbiting just 0.55 light-years to the Milky Way’s central black hole, Sagittarius A*, still forms silicate dust and harbors water molecules despite the galaxy’s most extreme radiation environment.
Mid-infrared images of the IRS 3 environment observed by VLT/NACO and Webb/MIRI/MRS. Image credit: Peiscar othersdoi: 10.1051/0004-6361/202660243.
At the center of the Milky Way, Sagittarius A* rules over a violent region of intense radiation, powerful winds, and gravitational stress.
Astronomers have long wondered how the fragile molecules and dust particles that are the raw material for planets, and eventually life, can survive in such close proximity to such environments.
“The galactic center is one of the most extreme environments, so understanding whether stars can continue to enrich their surroundings is an important question,” said Dr. Florian Peisker, 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 surprisingly resilient.”
IRS 3 is a red giant star, about 72 million years old and about six times the mass of the Sun.
The star is nearing the end of its life, shedding layers of gas and dust in a stage astronomers call the asymptotic giant branch.
Dr. Peisker and his colleagues used Webb’s MIRI (Mid-Infrared Instrument) to produce the most complete infrared spectrum of a star ever recorded, solving long-standing questions about stellar chemistry.
Previous ground-based observations left open the possibility that IRS 3 is carbon-rich, but the new Webb data shows two clear absorption signatures produced only by oxygen-rich silicate-based dust.
This combination rules out a carbon-dominated composition and firmly classifies IRS 3 as an oxygen-rich giant.
Perhaps even more shocking, astronomers detected distinct traces of water molecules in the material surrounding the star.
Water and other complex molecules are notoriously fragile and are easily broken down by the type of ultraviolet and X-ray radiation that falls from the region around a black hole.
The discovery of intact water so close to the galactic center suggests that the star’s dusty envelope is thick enough to protect sensitive chemicals from the harsh environment.
ESA astronomer Dr Macarena García Marín said: “This discovery was made possible thanks to Webb’s sophisticated infrared instruments.”
“This is the first time a continuous mid-infrared spectrum has been collected for this star, allowing us to detect features in the silicate dust and reveal the star’s true chemical identity.”
To interpret the spectra, the researchers used a radiation transport code called Hyperion to build a computer model of the shell of gas and dust around the star, testing about 100,000 variations before deciding on the optimal value.
The model shows a star about 60,000 times brighter than the Sun and an envelope organized into multiple concentric shells, each with a different temperature, density, and dust composition. Hot aluminum oxide close to the star gives way to cooler silicate grains farther away, with a temperature drop of approximately 1,000 K across the structure.
“The detection of water is particularly exciting because it shows that molecular materials can survive in environments dominated by intense radiation,” says Dr. Macarena.
“This shows that even near a supermassive black hole, a star can continue to return material to its surroundings.”
of result appear in the diary astronomy and astrophysics.
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F. Peisker others. 2026. Dust generation in harsh environments of Sgr A*. MIRI/JWST observation of O-rich asymptotic giant branch star IRS 3. A&A 712, A79; doi: 10.1051/0004-6361/202660243
Source: www.sci.news
