RESOLVING THE LEDGER
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The heart of the Milky Way may be more hospitable to water than astronomers thought.
Using the James Webb Space Telescope (JWST), researchers detected water and cosmic dust around an aging star only 0.55 light-years from Sagittarius A* (Sgr A*), the supermassive black hole at the center of our galaxy.
The new study suggests that water and dust can form and survive surprisingly close to a supermassive black hole , where intense radiation and other harsh conditions might otherwise be expected to destroy them. The team used Webb's Mid-Infrared Instrument (MIRI) to study IRS 3, an aging star located in the crowded environment surrounding Sgr A*, which has a mass of about 4 million suns, according to a statement from the European Space Agency (ESA).
(Image credit: ESA/Webb, NASA & CSA, F. Peißker, J. Lu, F. Yusef-Zadeh, N. B. Sabha, C. Chan)
"Galactic centres are among the most extreme environments, so understanding whether stars can continue enriching their surroundings there is an important question," Florian Peißker, lead author of the study from the University of Cologne in Germany, said in the statement . "With Webb, we can directly observe how stars behave under these conditions and see that dust production remains remarkably resilient."
IRS 3 — one of the brightest mid-infrared sources in the galactic center — is an asymptotic giant branch star , meaning it has reached a late stage of stellar evolution in which it sheds large amounts of gas and dust through powerful stellar winds. Such dying stars act as cosmic recycling centers, returning material to space that can eventually become incorporated into future generations of stars and planets.
But IRS 3 lives in a particularly unforgiving neighborhood. The center of the Milky Way is densely packed with stars and exposed to intense radiation, raising questions about whether molecules and newly produced dust can persist there.
However, Webb's observations suggest they can. By combining observations of IRS 3's spectrum with simulations of how its light travels through different models of the surrounding material, researchers reconstructed the structure of the star's envelope. They found a layered, shell-like distribution of silicate dust extending roughly 10,000 astronomical units from the star (one astronomical unit, or AU, is the average distance between Earth and the sun ). Temperatures within the envelope fall from about 1,700 degrees Fahrenheit (927 degrees Celsius) near the star to around minus 280 F (minus 173 C) in its outer regions. Webb's observations also revealed clear evidence of water within the envelope — the first such detection for IRS 3.
"The detection of water is especially exciting because it shows that molecular material can survive in an environment dominated by intense radiation," Macarena Garcia Marin, co-author of the study and an ESA astronomer, said in the statement.
While the observations don't reveal how much water is present, the detection shows that water can survive in the harsh environment near the galactic center . Water and dust are important ingredients in the chemistry that accompanies star and planet formation, meaning material shed by aging stars such as IRS 3 could eventually contribute to future generations of stars and planets.
Finding water and dust near Sgr A* therefore suggests that aging stars can continue enriching their surroundings even in the harsh conditions near a supermassive black hole. The findings could help astronomers better understand how material is recycled in the centers of galaxies and the role evolved stars play in supplying those regions with fresh dust and molecules.
Their findings were published Aug. 11 in the journal Astronomy & Astrophysics.
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