Just half a light-year from the supermassive black hole at the centre of the Milky Way, astronomers have found a star that keeps producing dust and water — the raw materials that could one day form new stars and planets. The discovery, made with the James Webb Space Telescope by an international team, reshapes how astronomers think about galactic centres, long considered too hostile for such processes.
The star IRS 3 lies just 0.55 light-years from Sagittarius A*, the supermassive black hole governing the motion of stars in the Galaxy's central region. It is one of the brightest mid-infrared sources in the galactic centre, long known for its enormous dusty envelope. IRS 3 is in a late stage of stellar evolution called the asymptotic giant branch, when stars become huge, cool and luminous, shedding gas through powerful stellar winds. This cast-off material is one of the most important sources of cosmic dust in the universe. But it remained unclear whether a star so close to a supermassive black hole could still produce it.
What Webb's spectrum revealed
Researchers analysed the star's infrared light using the Mid-Infrared Instrument (MIRI). For the first time, a continuous mid-infrared spectrum was collected for IRS 3, allowing the team to identify two strong spectral signatures associated with silicate dust — a compound of silicon and oxygen.
Previous studies had suggested IRS 3 was carbon-rich. The new data overturn that assumption: the star turns out to be oxygen-rich, nearing the end of its life and actively shedding material into space.
“This discovery was possible because of Webb's highly capable infrared instruments,” said Macarena Garcia Marin of ESA, a co-author of the study and principal investigator of the MICONIC programme. “This is the first time a continuous mid-infrared spectrum has been collected for this star, allowing us to detect the features from the silicate dust and uncover the star's true chemical identity.”
Water in an extreme environment
The most surprising result was the detection of water within IRS 3's surrounding envelope — the first clear finding 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. This tells us that even close to a supermassive black hole, stars can continue contributing material back into their surroundings.Macarena Garcia Marin, ESA
Lead author Florian Peißker of the University of Cologne noted: “Galactic centres are among the most extreme environments, so understanding whether stars can continue enriching their surroundings there is an important question. With Webb, we can directly observe how stars behave under these conditions and see that dust production remains remarkably resilient.”
The envelope's structure and the star's parameters
By combining the observed spectrum with models of how the star's light travels through different possible envelope structures, the team reconstructed its shape. The results point to a layered, shell-like distribution of dust extending roughly 10,000 astronomical units from the star. Temperature falls from about 1,200 kelvin close to the star to around 100 kelvin in the outer regions.
Based on the observations and stellar modelling, the researchers estimate IRS 3's mass at roughly six times that of the Sun, with an age of about 72 million years. The star is undergoing intense mass loss, ejecting material into space and building the extended envelope Webb detected.
What this means for galactic centres
The findings suggest that evolved stars may continue to play an important role in supplying dust to galactic centres — regions previously thought especially hostile to such processes. The observations were obtained in 2025 as part of the Guaranteed Time Observations programme MICONIC (Mid-Infrared Characterisation of Nearby Iconic galaxy Centres) using Webb's MIRI instrument. The results have been published in Astronomy and Astrophysics.
