JWST found water at Sagittarius A*’s doorstep — galactic cores do chemistry after all

The star IRS 3 should not be making water. It orbits 0.55 light-years from Sagittarius A*, the supermassive black hole at the Milky Way’s core — a zone so saturated with ultraviolet and X-ray radiation that most molecules are expected to be destroyed before they fully form. Yet data from the James Webb Space Telescope’s MIRI instrument show IRS 3 surrounded by a dense envelope containing both water vapor and oxygen-rich silicate dust, exactly the kinds of molecular material that dying stars produce far from such radiation sources.

Florian Peißker at the University of Cologne led the detection, which overturns a long-held assumption: that the extreme environment immediately surrounding supermassive black holes acts as a chemistry-free zone, too violent to allow the molecular processes that populate calmer stellar neighborhoods. IRS 3 shows the process happening anyway. How many other evolved stars near galactic centers are quietly doing the same thing is a question the full MICONIC survey is now positioned to answer.

How JWST read the chemistry inside the Milky Way’s most extreme zone

Peißker’s team used JWST’s Mid-Infrared Instrument (MIRI) to observe the innermost parsec surrounding Sagittarius A*. Mid-infrared wavelengths reveal what optical telescopes cannot: the thermal glow of dust and the molecular absorption features of compounds like water. Previous instruments either lacked the resolution to separate IRS 3 from its neighbors or lacked MIRI’s sensitivity at the relevant wavelengths.

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The data showed two distinct spectral signatures inside IRS 3’s dusty envelope: the fingerprint of oxygen-rich silicate dust (a compound of silicon and oxygen) and the unmistakable absorption feature of water vapor. These are not trace detections. The team ran multiple models of the stellar envelope’s structure, comparing different temperature profiles, dust compositions, and geometric configurations, and the signatures persisted across all of them. The work was conducted under MICONIC, a JWST program designed specifically to map the galactic center at mid-infrared wavelengths.

An Earth mass of enriched material shed every 18 days

IRS 3 is an oxygen-rich asymptotic giant branch (AGB) star — a class of evolved red giants in the final chapters of their lives. Stars at this stage have exhausted the helium-burning fuel in their cores and are shedding their outer layers in increasingly intense stellar winds. IRS 3 is currently in what astronomers call the superwind phase: the period of maximum mass-loss immediately before a star expels its outer shell entirely and collapses into a white dwarf.

The mass-loss rate is extraordinary even by AGB standards: the star ejects the equivalent of one Earth mass of material every 18 days. At the stellar wind velocity of 15 kilometers per second, this material has built up into a dusty envelope extending roughly 10,000 astronomical units from the star — about 250 times the distance from Earth to Neptune. The innermost region of this envelope sits at around 1,200 Kelvin, cool enough for silicate grains to condense; the outer fringes cool to about 100 Kelvin. At both extremes, the material has survived despite the radiation field maintained by Sagittarius A* and the dense cluster of young, hot stars nearby.

The star itself is roughly 6 times more massive than the Sun and shines at about 60,000 times solar luminosity. It is 72 million years old — a short lifespan, consistent with a massive star that burned through its fuel fast.

What this changes about galactic center chemistry

For decades, galactic centers have been treated as chemically stunted regions. The argument was straightforward: intense radiation from the central black hole and its surrounding activity dissociates molecules faster than they can form. Studies of dust formation in AGB stars consistently placed these objects in quiet neighborhoods far from galactic nuclei.

The MICONIC observation suggests that picture was incomplete. Even a fraction of a light-year from one of the most active points in the Milky Way, a star in its final life stage is still doing the chemical work that AGB stars do everywhere: condensing silicate dust, incorporating oxygen into molecular bonds, building water in its outer atmosphere. If IRS 3 is representative of evolved stars orbiting near galactic centers — not a unique exception but a member of a population — galactic nuclei may be receiving a steady input of complex molecules from the evolved stellar population circling within them.

The implications extend beyond the Milky Way. Supermassive black holes sit at the center of most large galaxies, many surrounded by dense stellar populations. JWST is now capable of probing those environments at mid-infrared wavelengths. Whether IRS 3-type chemistry operates near the black holes of other galaxies is a question the telescope is directly equipped to answer.

What the study leaves unresolved

The detection inside IRS 3’s envelope is solid, but what happens to the material once it leaves the star is harder to determine. The dense stellar wind may provide local shielding that keeps molecules intact close to the star, while the surrounding radiation destroys them within a small additional distance. Whether the dust and water from IRS 3 mix into the broader galactic center environment — or are rapidly photodissociated beyond the stellar cocoon — requires monitoring the fate of the ejected material over time.

The models used to interpret the infrared signatures carry inherent uncertainties. AGB stars at the galactic center exist in a radiation environment unlike anything modeled for stellar populations in the solar neighborhood. The team’s best-fit models match the observations well, but the actual dust grain size distribution and three-dimensional structure of the envelope remain constrained within ranges rather than pinned to single values.

IRS 3 is also one star. Whether the result generalizes depends on the full MICONIC survey’s completion.

Questions about water forming near a black hole

How can water survive next to a supermassive black hole? The key is IRS 3’s envelope. The star’s dense outer atmosphere provides a local cocoon dense enough to shield the innermost regions from Sagittarius A*’s radiation. Molecules form where the gas is cool and dense, protected by the surrounding material from direct exposure to the most energetic photons. Whether that shield holds beyond the immediate stellar environment remains an open question.

What is 0.55 light-years in practical terms? About 35,000 times the Earth-Sun distance — enormous in any human frame, but a small fraction of a light-year places IRS 3 closer to Sagittarius A* than the nearest star to our own Sun. Proxima Centauri sits 4.2 light-years from us; IRS 3 orbits at a distance roughly eight times smaller than that from the most massive object in the Milky Way.

What is the superwind phase? AGB stars experience increasing mass-loss as they age. The superwind phase is the final burst of this process — when the star ejects material at a rate hundreds or thousands of times higher than earlier in its life. Once the superwind ends, the star has shed most of its outer layers and the remnant collapses into a compact white dwarf.

Does this mean water could exist near other galactic black holes? The finding makes it plausible. The mechanism — an evolved star shielding its own molecular envelope against surrounding radiation — is not unique to the Milky Way. Whether similar chemistry operates near other galactic supermassive black holes is now a testable question, and JWST’s mid-infrared capabilities make it the instrument best placed to test it.

Peißker and colleagues published their findings in Astronomy & Astrophysics in August 2026. The MICONIC survey will continue mapping the galactic center over the coming months, targeting other evolved stars and sources in the inner parsec. Whether IRS 3’s chemistry represents an isolated case or the first confirmed instance of a broader process operating inside galactic cores is the question the survey is designed to answer.

Reference: Peißker et al., “Dust production in the harsh environment of Sgr A* — MIRI/JWST observation of the O-rich asymptotic giant branch star IRS 3,” Astronomy & Astrophysics, 2026. DOI: 10.1051/0004-6361/202660243

Tags: astronomy, JWST, black holes, Sagittarius A*, galactic center, IRS 3

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