NASA’s James Webb Space Telescope has detected water vapor and silicate dust within the expanding envelope of star IRS 3, located just 0.55 light-years from the supermassive black hole Sagittarius A* at the center of the Milky Way, challenging long-held assumptions about chemical survival in galactic core environments.
Deep in the galactic center, where radiation and gravitational forces dominate, astronomers have uncovered molecules that conventional models suggested could not survive. The discovery centers on IRS 3, an aging star completing its stellar lifecycle approximately 0.55 light-years—or about 42,000 astronomical units—from the central supermassive black hole known as Sagittarius A*.
Stellar Mass Loss Near Sagittarius A*
IRS 3 sits in an extreme cosmic neighborhood. Previous scientific assumptions held that the intense ultraviolet and X-ray radiation originating from the accretion disk of Sagittarius A* would tear apart complex molecules and prevent dust from forming. Yet observations show that the star is actively shedding its outer layers, hurling stellar material outward at a massive rate.
The star has an estimated mass of about six solar masses and an age of roughly 72 million years. According to observational data, IRS 3 ejects material equivalent to the mass of Earth every 18 days. This ongoing mass loss creates a vast, layered envelope extending outward to roughly 10,000 astronomical units from the star.
Mid-Infrared Observations with MIRI
To peer through the dense dust obscuring the galactic center, researchers utilized the Mid-Infrared Instrument aboard the James Webb Space Telescope. The instrument revealed that IRS 3 belongs to the asymptotic giant branch phase of stellar evolution, a stage where aging stars expand, cool, and generate powerful stellar winds.
Spectral data captured by MIRI identified distinct signatures of silicate dust, confirming that IRS 3 is an oxygen-rich star rather than a carbon-rich object as earlier models suggested. Most notably, the instrument detected clear signs of water vapor within the expanding circumstellar shell.
Thermal modeling of the structure indicates that temperatures within the envelope drop steeply from approximately 1,200 Kelvin near the stellar surface down to around 100 Kelvin at the outer boundaries.
Implications for Galactic Chemical Evolution
Finding water and silicate dust so close to a supermassive black hole alters the understanding of how heavy elements and molecules distribute through galactic nuclei. The survival of water molecules in an environment subjected to heavy radiation demonstrates that stellar envelopes can act as protective cocoons.
This resilience suggests that evolved stars contribute significantly more to the chemical enrichment of central galactic regions than researchers previously calculated. The data indicate that molecular material can persist even under the harsh conditions dictated by a nearby black hole.
Future Instrumentation and Next Steps
Astronomers plan to examine the region with even higher precision. Future observations will utilize the METIS instrument, a next-generation tool currently being developed at the Institute of Astrophysics at the University of Cologne for the Extremely Large Telescope situated in the Atacama Desert in Chile. These upcoming studies aim to map the physical dynamics of the IRS 3 shell and clarify how molecular compounds endure near the heart of the Milky Way.
