The center of our Mich Street system may have visitors from far reaches of space: some of the stars orbiting the central black hole did not form on our global island. A team led by Shogo Nishiyama of Miyagi University of Education came to this conclusion after observing the star SO-6, which orbits the supermassive black hole at a distance of only 0.04 light-years. As the working group now reports in the professional journal “Proceedings of the Japan Academy.”The chemical composition does not match that of the Milky Way system, but rather matches that of dwarf galaxies such as the Small Magellanic Cloud. This means that SO-6 has traveled at least 50,000 light-years during its existence – and perhaps much further.
There are many stars in the vicinity of Sagittarius A*, the supermassive black hole at the center of the Milky Way. But they could not have formed there, as massive tidal forces prevent clouds of gas from clumping to form protostars. So they must have migrated there from other areas. But from where? Are they nearby stars that have gradually slipped into an ever tighter orbit due to interactions with their surroundings? Or perhaps it was thrown from a distant spiral arm into the center of the galaxy during a close encounter with another star?
Research conducted by Nishiyama’s team suggests that the reality is even stranger. For eight years, experts have observed SO-6 using the Subaru telescope on Mauna Kea in Hawaii. They measured its speed and acceleration to prove that the star is indeed close to the black hole and does not appear only in this way. They also used its spectrum to determine the absorption lines of the star’s atmosphere in order to determine the proportions of distinct elements that allow conclusions to be drawn about its age and origin. Therefore, it does not come from the central region of the Milky Way system, but from a satellite galaxy. The most likely explanation, according to the team, is that SO-6 once formed into a small companion of the Milky Way that eventually swallowed it.
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