Webb Showcases How IRS 3 Still Makes Dust and Water 0.55 Light-Years From Sagittarius A*

Webb’s NIRCam and MIRI cameras filled a 2.5-by-1.8-arcminute frame with the inner parsec of the Milky Way, a packed star field 26,000 light-years away in Sagittarius. IRS 3 sits in that crowd, a cool, luminous asymptotic giant branch star only 0.55 light-years from Sagittarius A*, the four-million-solar-mass black hole at the center of the galaxy. NASA posted the composite on September 10, 2026, from data taken August 11. Mid-infrared light from the same field had already given astronomers something they had never measured cleanly for this object: oxygen-rich silicate dust and water molecules in the star’s own envelope.

The IRS 3 gained its name the traditional way: by standing out from the crowd. Infrared studies of the galactic center have designated the brightest mid-infrared spots in sequence, and IRS 3 was the most prominent AGB star within the inner parsec, as well as in the surrounding area. Earlier work had left the chemistry as a mystery. Some data showed it might be carbon-rich, but no one knew for sure. MIRI’s Medium Resolution Spectrometer delivered the goods in 2025 as part of the MICONIC guaranteed-time initiative. It offered the team the first continuous mid-infrared spectrum of the star, from around 5 to 28 microns. After correcting for all of the foreground dust, the two significant absorption bands emerged: a broad Si-O stretch at 9.7 microns and an O-Si-O bend at 18.5 microns. These properties are typical of amorphous silicates, which also contain alumina. After calculating the statistics, the optical-depth ratio of the two silicate bands came out to be 3.5, which pretty well sealed the deal: IRS 3 is oxygen-rich.

Florian Peißker of the University of Cologne led the study, which was published in Astronomy & Astrophysics. According to the models, the star has around six times the mass of our Sun and is approximately 72 million years old. Its luminosity is almost 60,000 times that of the Sun, and its effective temperature is only 2,800 K. It’s shedding its outer coats in a wind gusting at about 15km/s. The mass loss is estimated to be 6 × 10⁻⁵ solar masses per year. This material is forming a shell-like envelope that spans 10,000 astronomical units. Temperature is lowering from around 1,200 K near the star to approximately 100 K in the outer portions, which indicates hot alumina is hanging out in the core bits and cooler silicate grains are taking over in the outer shells.

Then there is the water. Yes, it appeared on the same spectrum. Absorption at 6.00-6.25 microns and near 6.7 microns corresponds to H₂O transitions observed in the laboratory. According to models, water is located in the inner envelope at a few hundred astronomical units and has a temperature of approximately 700 K. This is the true thing: molecule water in gas and dust, not lakes or ice sheets on any planet. This is the first time anyone has seen it clearly in the IRS 3 spectrum. According to ESA’s Macarena Garcia Marin, the principle investigator on MICONIC, the continuous mid-infrared record allowed the silicate bands and water features to shine through against the background of the galactic center.

The galactic center emits a variety of radiation, including ultraviolet and X-rays, and it was once thought that dust grains and weak molecules could not withstand it. But IRS 3 is simply humming along, producing both. The fresh silicate dust and water molecules are leaving the star and traveling directly into the interstellar medium, only a fraction of a light-year away from the black hole. You’re aware that these types of stars are steadily populating the galaxy with raw material for new stars and planets, and this Webb data simply demonstrates that the same factory is still operating in one of the Milky Way’s harshest neighborhoods.