Webb reveals oxygen-rich dust and water surviving near Milky Way’s central black hole

Using the NASA/ESA/CSA James Webb Space Telescope, an international team of astronomers has discovered that dust and water can form and survive surprisingly close to the supermassive black hole at the center of the Milky Way galaxy. The observations reveal that the evolved star IRS 3 continues to enrich its surroundings with newly formed material despite the intense radiation environment around Sagittarius A*.

IRS 3 has reached a stage near the end of its life called the asymptotic giant branch phase. Stars in this phase of life are huge, cool and luminous, and they shed gas into space with their powerful stellar winds. This cast-off stellar material is one of the most important sources of cosmic dust, but it was not clear whether it could be produced by a star so close to a supermassive black hole.

Webb clarifies the star’s chemistry

By analyzing the star’s infrared light with Webb’s Mid-Infrared Instrument (MIRI), the research team identified clear signatures of oxygen-rich dust and, for the first time, detected water in the star’s surrounding envelope. The results show that even under the harsh conditions near a supermassive black hole, evolved stars like IRS 3 can still produce dust and other materials important for the creation of future generations of stars and planets.

“Galactic centers are among the most extreme environments, so understanding whether stars can continue enriching their surroundings there is an important question,” said lead author Florian Peißker of the University of Cologne in Germany. “With Webb, we can directly observe how stars behave under these conditions and see that dust production remains remarkably resilient.”

The paper is published in the journal Astronomy & Astrophysics.

IRS 3 is one of the brightest mid-infrared sources in the galactic center and has long stood out because of its enormous dusty envelope. Previous studies suggested the star could be carbon-rich, but the new observations paint a different picture. The Webb data revealed two strong infrared signatures associated with silicate dust, which is composed of silicon and oxygen. These features identify IRS 3 as an oxygen-rich evolved star nearing the end of its life and shedding material into space.

“This discovery was possible because of Webb’s infrared instruments,” said Macarena Garcia Marin of ESA, a co-author of the study and PI of the MICONIC program. “This is the first time a continuous mid-infrared spectrum has been collected for this star, allowing us to detect features of the silicate dust and uncover the star’s true chemical identity.”

A layered envelope comes into view

By combining Webb’s observations of the star’s spectrum with simulations of how its emitted light would move through different models of the surrounding envelope, the team was able to reconstruct the structure of the star’s envelope. Their results indicate a layered, shell-like distribution of dust extending roughly 10,000 astronomical units from the star, with temperatures falling from approximately 1,200 Kelvin (1,700°F) close to the star to around 100 Kelvin (-280°F) in the outer regions. The observations also revealed evidence for water within the envelope of IRS 3: the first clear detection of its kind for this object.

“The detection of water is especially exciting because it shows that molecular material can survive in an environment dominated by intense radiation,” said Garcia Marin. “This tells us that even close to a supermassive black hole, stars can continue contributing material back into their surroundings.”

From the observations and stellar modeling, the researchers estimate that IRS 3 has a mass of approximately six times that of the sun and is around 72 million years old. The star appears to be undergoing intense mass loss, ejecting material into space and creating the extended envelope seen by Webb.

Dust survives where few expected it

These results suggest that evolved stars may continue playing an important role in supplying dust to galactic centers—regions that were previously thought to be especially hostile to these processes.

The observations were obtained in 2025 as part of the Mid-Infrared Characterization of Nearby Iconic galaxy Centers (MICONIC) Guaranteed Time Observations program (#1266) using Webb’s MIRI instrument.

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Swati Mestri

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Robert Egan

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