After eight years of observing a star at the very center of our Milky Way galaxy, Japanese scientists have concluded that it originated from another galaxy. This is the first confirmed observation of such an object. Now, scientists need to uncover more details about the mysterious star and its system.
The S-type star, designated as S0-6, was discovered in the vicinity of the supermassive black hole Sagittarius A* at the center of our galaxy. S-type stars typically move along highly elongated, long-period orbits. S0-6 was no exception, but its orbit around the black hole was only at a distance of 40,000 light-years. Extended observations of the star confirmed its trajectory around the black hole. Since the surroundings of black holes are not conducive to star formation, it suggests that this star arrived there from another place. But from where?
The answer to this question was facilitated by the spectral analysis of the star's light. Firstly, the presence of heavy element lines and their intensity in the spectrum allows conclusions to be drawn about the star's age. The fewer heavy elements it contains, the older the star. Astronomers estimated the age of S0-6 at 10 billion years. It is only 3 billion years younger than the Milky Way. Secondly, spectral analysis reveals the chemical composition of the object. The chemistry of S0-6 is significantly different from other stars in the explored region of space. This indicates that the star was born elsewhere and was captured by the black hole at the center of our galaxy only after a considerable amount of time.
The chemical composition of S0-6 turned out to be similar to the composition of stars from dwarf galaxies surrounding the Milky Way. Thus, scientists believe that it arrived from another galaxy, which should not be surprising. Over its history, the Milky Way has absorbed several dwarf galaxies, and a star from one of them could have made its way to the center and been captured by the supermassive black hole.