Just 0.17 parsec from the Milky Way’s central black hole, or about 0.55 light-year, an old star remains surrounded by an immense envelope of dust. James Webb also detected the signature of water vapor there. These observations show that fragile materials can survive and form in this region exposed to intense radiation.
The object studied, called IRS 3, is not the black hole itself. It is an aging star located near Sagittarius A*, the supermassive black hole at the center of our galaxy. Having reached an advanced stage of its life, it is gradually ejecting some of its material into space.
Mid-infrared image of the environment around IRS 3. A yellow cross marks the supermassive black hole Sgr A*
This material forms an envelope around IRS 3 whose radius reaches approximately 10,000 times the distance between Earth and the Sun. As it moves away from the star, the gas cools and some elements condense into tiny solid grains. This process contributes to the formation of the dust later found between the stars.
The proximity of the galactic center makes this case unusual. Millions of stars occupy this region, where ultraviolet radiation can destroy or alter molecules and dust grains. Astronomers therefore wanted to know whether IRS 3 was actually able to produce dust in this environment.
James Webb observed IRS 3 in April 2025 with MIRI, its instrument dedicated to the mid-infrared. By separating light according to its wavelength, scientists can identify materials through the features they leave in the spectrum. They thus studied light between 4.9 and 27.9 micrometers.
The data indicate that IRS 3 is an oxygen-rich star, unlike an earlier classification that described it as carbon-rich. The models reproduce its envelope with alumina in the hottest regions and silicates farther out. These silicates are minerals containing, among other elements, silicon and oxygen, and are widespread in cosmic dust.
Another feature appears around 6.1 to 6.25 micrometers. The authors primarily associate it with water vapor, after comparing it with known molecular signatures. They estimate this component’s temperature at about 427 °C. This is the first reported detection of water around IRS 3.
The models indicate that IRS 3 produces these dust grains and molecules itself as it loses material. This shows that an old star can still supply its surroundings with solid grains very close to the galactic center.
One question remains open: why does IRS 3 have such a prominent envelope when other comparable old stars appear to be rare in this region? The authors notably suggest the influence of the surrounding medium and the possibility of previously unknown interactions. Future observations will have to determine how this envelope evolves under the conditions around Sagittarius A*.