The James Webb Space Telescope has made a groundbreaking discovery: water molecules surrounding a dying star near the Milky Way's central black hole, Sagittarius A*. This star, IRS 3, is an asymptotic giant branch (AGB) star, known for its massive dust envelope and rapid mass loss. The findings challenge previous assumptions about the survival of stellar envelopes in such extreme environments and offer new insights into the behavior of AGB stars near supermassive black holes.
IRS 3's dusty envelope, extending 10,000 astronomical units, is remarkably large and well-preserved despite its proximity to Sagittarius A*. The star's mass loss rate, estimated at 6 × 10^-5 solar masses per year, is incredibly high, equivalent to the mass of Earth every 18 days. This rapid shedding of material has allowed IRS 3 to maintain its dense, expanding envelope, even in the harsh conditions of the Galactic center.
The James Webb observations revealed an oxygen-rich star with silicate dust, multiple shells of expelled material, and clear water signatures. The detection of water is significant because it suggests that molecular material can survive in the intense radiation and interactions near Sagittarius A*. This challenges the notion that stellar envelopes are completely destroyed in such environments.
The study also found that the envelope is not a simple cloud but consists of multiple shells at different temperatures and distances. These shells may record thousands of years of the star's mass-loss history, providing valuable insights into the star's evolution. The researchers estimated the density of surrounding material and found evidence of highly uneven conditions in the inner Galactic center.
The findings have practical implications for astronomers. IRS 3 offers a rare glimpse into how AGB stars can produce and preserve dust near a supermassive black hole. Its high mass loss rate could replenish material in the immediate surroundings of Sagittarius A*, and the detection of water suggests that molecules can persist inside a sufficiently dense stellar envelope, even in the challenging environment of the Galactic center.
Future observations, such as those planned for the Extremely Large Telescope with METIS, will further enhance our understanding of IRS 3 and AGB stars in the Galactic center. These studies will probe the star's structure in greater detail and help distinguish between various mechanisms, including stellar outflows, interactions with surrounding gas, and gravitational effects from Sagittarius A*.
