Water found 0.55 light-years from the Milky Way's black hole, in a dying star's shell

Astronomers report traces of water inside the shed envelope of IRS 3, an aging star that sits 0.55 light-years from Sagittarius A*, the Milky Way's supermassive black hole ^[1][2]. Water has been found around other stars, but never this close to the galactic center, and the result cuts against the assumption that the region is too extreme for old stars to keep seeding their surroundings with dust and molecules ^[1][5].

The work was described on Aug. 11 in the journal Astronomy & Astrophysics, alongside an image of the region assembled from the James Webb Space Telescope's Near-Infrared Camera and Mid-Infrared Instrument ^[4][7]. IRS 3 lies about 26,000 light-years from Earth and is shedding gas and dust into a sprawling envelope around itself ^[3][14]. It belongs to the asymptotic giant branch, the late phase in which large, cool, luminous stars blow off their own layers through stellar winds and seed the surrounding medium with dust ^[9]. Whether a star that close to Sagittarius A* could still drive those winds and make dust was, until now, unresolved ^[10].

The mechanics matter more than the headline molecule. According to the team, this is the first continuous mid-infrared spectrum collected for IRS 3, which is what made the silicate dust features legible and, in study co-author Macarena Garcia Marin's phrasing, uncovered the star's true chemical identity ^[8]. Two strong silicate signatures, silicon plus oxygen, point to oxygen-rich chemistry, overturning an earlier classification of IRS 3 as carbon-rich that had rested on the shape of its dust envelope rather than on spectroscopy ^[12]. That is a reversal of chemistry, not a refinement of it, and it is the kind of correction that continuous spectra tend to produce when they replace inference from morphology.

Pairing the spectra with models of how starlight propagates through candidate dust geometries, the team's best fit is a layered, shell-like envelope extending roughly 10,000 astronomical units, with temperatures falling from about 1,200 kelvins near the star to about 100 kelvins at the outer edge ^[11]. That is a factor of twelve across the structure ^[1], and the water sits inside it. Garcia Marin, a researcher at the European Space Agency and principal investigator of the Mid-Infrared Characterization of Nearby Iconic galaxy Centers program, said the detection is notable because it shows molecular material can survive in an environment dominated by intense radiation ^[6][8].

The stellar parameters are modest for such an aggressive setting: roughly six solar masses, an age of about 72 million years, and a luminosity around 60,000 times the sun's ^[13], which is on the order of 10,000 times the sun's output per unit mass ^[2].

Watch whether the same continuous mid-infrared treatment revises the chemistry of other dust-producing stars in the central region, since classifications built on envelope shape have now been shown to fail at least once ^[12]. Watch, too, whether dust budgets for galactic nuclei get rewritten if old stars there are contributing after all ^[5].