Using data from the NASA/ESA/CSA James Webb Space Telescope, astronomers found that IRS 3 — a bloated giant star orbiting just 0.55 light-years to Sagittarius A*, the Milky Way’s central black hole — is still forging silicate dust and harboring water molecules despite the Galaxy’s most extreme radiation environment.
Mid-infrared image of the IRS 3 environment, observed with VLT/NACO and Webb/MIRI/MRS. Image credit: Peißker et al., doi: 10.1051/0004-6361/202660243.
At the heart of the Milky Way, Sagittarius A* dominates a violent neighborhood of intense radiation, powerful winds and gravitational stress.
Astronomers have long wondered how fragile molecules and dust grains — the raw material for planets and, eventually, life — could possibly survive so close to such an environment.
“Galactic centers are among the most extreme environments, so understanding whether stars can continue enriching their surroundings there is an important question,” said Dr. Florian Peißker, an astronomer at the University of Cologne.
“With Webb, we can directly observe how stars behave under these conditions and see that dust production remains remarkably resilient.”
IRS 3 is a red giant around 72 million years old and is about 6 times the mass of the Sun.
The star is nearing the end of its life, puffing off layers of gas and dust in a phase astronomers call the asymptotic giant branch.
Using Webb’s MIRI (Mid-Infrared Instrument), Dr. Peißker and his colleagues produced the most complete infrared spectrum of the star ever recorded, which settles a long-standing question about the star’s chemistry.
Earlier ground-based observations had left open the possibility that IRS 3 was carbon-rich, but the new Webb data show two telltale absorption features that are produced only by oxygen-rich, silicate-based dust.
This combination rules out a carbon-dominated composition and firmly classifies IRS 3 as an oxygen-rich giant.
Perhaps more striking, the astronomers detected clear signatures of water molecules in the material surrounding the star.
Water and other complex molecules are notoriously fragile, easily broken apart by ultraviolet and X-ray radiation of the kind that pours out of the region around a black hole.
Finding intact water so close to the Galactic center suggests that the star’s dusty envelope is thick enough to shield delicate chemistry from its harsh surroundings.
“This discovery was possible because of Webb’s highly capable infrared instruments,” said Dr. Macarena Garcia Marin, an astronomer at ESA.
