Dust and water in the vicinity of the central black hole
An unexpected discovery: Water and dust have been detected in the immediate vicinity of the black hole Sagittarius A* in our galaxy. Actually, the conditions in this region of space should not allow for such a thing.
About 26,000 light-years away, the galactic center lies in the constellation Sagittarius, where the massive black hole Sagittarius A* (Sgr A*) is located, containing 4.1 million solar masses. Extreme conditions prevail in its immediate vicinity, which is why a discovery by a research team led by Florian Peisker at the University of Cologne is causing astonishment: only about 0.55 light-years from Sgr A*, dust and water vapor released by the giant star IRS 3 have been detected. This shows that even in the extremely radiation-rich environment of an extremely massive black hole, stars can produce the building blocks of future generations of stars and planets.
The star is a red supergiant, relatively cool and very bright. It ejects large amounts of gas and dust through an extreme stellar wind, causing IRS 3 to shed a significant portion of its mass into the surrounding space. It has about six times the mass of our sun, is around 72 million years old, and is near the end of its existence as a member of the asymptotic giant branch in the Hertzsprung-Russell diagram.
This stellar outflow from red giants and supergiants is one of the most important sources of cosmic dust in our galaxy. Until now, however, it was not clear whether such a phenomenon was possible in the immediate vicinity of an extremely massive black hole. For their work, Peisker's team used the James Webb Space Telescope (JWST) to study the galactic center in detail in the infrared. Using the MIRI instrument on board the JWST, clear signatures of oxygen-rich dust and, for the first time, water molecules were detected in the shell surrounding IRS 3.
In the mid-infrared, IRS 3 is one of the brightest radiation sources in the vicinity of Sgr A* and attracted early attention due to its enormous dust envelope. Earlier investigations suggested that the star might be particularly carbon-rich, but this does not seem to be true according to the new data. Instead, two distinct signals of dust were found, which is apparently silicate-rich, meaning it contains oxygen and silicon. From this, it can be concluded that IRS 3 is an oxygen-rich, highly evolved star that has reached the end of its lifespan. From the data, the structure around IRS 3 can be derived up to a distance of 10,000 astronomical units, which corresponds to 10,000 times the distance from Earth to the Sun. The region is layered. Within the layers, the temperature drops from 900 degrees Celsius near the star to -170 degrees Celsius in the outer regions. In addition, water vapor was detected in these layers.
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