Dust and water can persist surprisingly close to the supermassive black hole at the center of the Milky Way, where an aging star is still shedding material into its surroundings despite the extreme radiation environment. Observations from the James Webb Space Telescope show that the evolved star IRS 3 is producing oxygen-rich dust and contains water in the envelope around it.
IRS 3 is one of the brightest mid-infrared sources in the Milky Way’s galactic center. Its large dusty envelope had already made it an unusual object, but its chemical identity was less certain.
Earlier observations had suggested that IRS 3 might be rich in carbon. Webb’s Mid-Infrared Instrument, or MIRI, provided a different picture.
The new infrared spectrum contains two strong features associated with silicate dust, a type of dust made from silicon and oxygen. These signatures identify IRS 3 as an oxygen-rich evolved star that is nearing the end of its life and losing material to space.
IRS 3 is in a late stage of stellar evolution known as the asymptotic giant branch phase. Stars at this stage are large, cool and luminous, and they can shed gas through powerful stellar winds. The material they release contributes to the dust found in space.
What was unclear was whether a star so close to the Milky Way’s central supermassive black hole could continue producing and releasing that material.
“With Webb, we can directly observe how stars behave under these conditions and see that dust production remains remarkably resilient,” lead author Florian Peißker of the University of Cologne in Germany said.
The dusty envelope has layers
The researchers combined Webb’s spectrum with simulations of how light would travel through different models of the material surrounding IRS 3. This allowed them to reconstruct the structure of the star’s extended envelope.
The results indicate that the dust is arranged in layers resembling shells and extends about 10,000 astronomical units from the star. The temperature changes substantially across the envelope. Near IRS 3, the material is estimated to be about 1,200 Kelvin, or 1,700°F. In the outer regions, temperatures fall to about 100 Kelvin, or -280°F.
The observations also produced another important result. Webb detected evidence of water in the envelope surrounding IRS 3.
This is the first clear detection of water reported 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 Macarena Garcia Marin of ESA, a co-author of the study and principal investigator of the MICONIC program.
An aging star is losing material
The observations and stellar modeling indicate that IRS 3 has a mass of about six times that of the Sun and is approximately 72 million years old.
The star appears to be undergoing intense mass loss. Material is being expelled into space, producing the large envelope observed by Webb.
The findings indicate that evolved stars can continue supplying dust to galactic centers even under the extreme conditions found near a supermassive black hole. They also provide evidence that molecular material such as water can remain present within the star’s surrounding envelope.
The observations were made in 2025 as part of the Mid-Infrared Characterization of Nearby Iconic galaxy Centers, or MICONIC, Guaranteed Time Observations program using Webb’s MIRI instrument.
The study was published in Astronomy & Astrophysics.
