German astronomers made the first map of the "dark side" of the Galaxy by observing the movement of alcohol and water molecules in spiral arms located behind the opaque core of the Milky Way, according to an article published in the journal Science.
“The Milky Way contains many 'stellar nurseries', many of which are cosmic masers. They will help us make an accurate map of the Galaxy, but this maser was really unique as it allowed us to look at the 'other side' of the Milky Way and see what is there,”said Karl Menten of the Institute of Radio Astronomy in Bonn (Germany).
The Milky Way is also one of the most studied spiral galaxies, and at the same time, we have almost no reliable data about how large it is, how its arms are arranged and how its stars are located relative to each other. All this happens for the reason that we cannot "fly" over the Galaxy and look at it from the side, like other "star megacities".
Another big obstacle to observing the Milky Way is that its core is surrounded by a huge amount of dust and gas, making it difficult to observe the stars in the center of the Galaxy and its arms, located on the opposite side of the Earth and the Sun. Therefore, today scientists know only a few dozen stars located behind the nucleus of the galaxy, and the structure of its arms on its "dark side" remained an absolutely unknown thing for them.
Menten and his colleagues at the institute found a way to solve this problem by discovering the first "cosmic" maser - a natural source of coherent microwave radiation, located not on the "visible" side of the Galaxy, like other objects of this kind, but on the other side of its core.
Observing the maser source with single telescopes does not allow calculating distances for it, and therefore scientists had to go to the trick. They observed some "suspicious" masers with the help of several radio telescopes located in different parts of the earth and united into a single virtual radio dish VLBA.
This is how the artist imagined the movement of water and methanol molecules in a “ dark ” side of the Milky Way / Illustration by RIA Novosti. Alina Polyanina
A signal from a maser or any other cosmic source, Menten explains, will arrive at each component of such a telescope with a slight delay, which allows us to calculate its position by observing similar masers at different times of the year when the Earth is in opposite points of its orbit.
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Guided by this idea, scientists measured signals from various cosmic masers until they came across the object G007.47 + 00.05, located, as it turned out, 66 thousand light-years from Earth, on the opposite edge of the Milky Way.
These "stellar nurseries", according to scientists, are located inside the spiral arm of the Centauri Shield, located behind the galactic core, whose existence some astronomers have doubted in the past.
Analyzing the data collected over the next two years of observations, scientists were able to reveal some details of its structure and understand that the degree of its "twist" can vary greatly with distance from the central part of the Milky Way, which contradicts current ideas about the structure of the Galaxy.
According to Menten, the detection of the G007.47 + 00.05 maser suggests that the Milky Way does indeed have four arms, not three, and the discovery of similar objects, scientists hope, will help us draw up a complete map of the "dark side" of the Galaxy and get its first realistic images.
