Astronomers have now discovered that a star near the supermassive black hole at the center of the Milky Way likely originated from a smaller galaxy that was swallowed up. There are more than 100 billion stars in the Milky Way, and while the vast majority of them were born and grew here, some appear to have migrated from other galaxies. Most of these interstellar immigrants appear in the "halo" of the Milky Way, located on the outer reaches of the Milky Way. But in a new study, Japanese astronomers have discovered a galaxy at the center of the Milky Way.
At the very center of the Milky Way, there is a supermassive black hole called Sagittarius A*. It's a seemingly active neighborhood, but it's thought that new stars aren't formed there very often because of the extreme force the monster exerts on its surroundings. Astronomers at Miyagi University of Education were studying where these stars migrated from, and they discovered that one of the stars had a much longer journey than expected.
The star, known as S0-6, is less than 11 light-years from the black hole. Astronomers have been observing its movements for eight years using the Subaru Telescope in Hawaii. Their research found that the star is more than 10 billion years old - and most curiously, it is an old man with extensive travel experience.
The chemical composition of the S0-6 star does not match that of other nearby stars or even stars within the Milky Way. Instead, it is more similar to the stars in the small galaxies that surround our Milky Way, such as the Small Magellanic Cloud and the Sagittarius Dwarf Galaxy. The researchers speculate that it seems to be a common occurrence for S0-6's parent galaxy to be swallowed up by the Milky Way, although these stars are not known to be swallowed up so deep in the Milky Way.
This origin story suggests that the star traveled at least 50,000 light-years to reach its current location. But the actual number is likely much higher because it spirals slowly over billions of years rather than in a straight line toward the center.
Of course, discovering S0-6's weirdness isn't the end of the story -- rather, it means astronomers will be motivated to study it more closely to help answer more questions.
"Did S0-6 really originate outside the Milky Way? Does it have companions, or is it traveling alone? Through further investigation, we hope to unravel the mystery of stars near supermassive black holes."
The paper of this research was published in Proceedings of the Japanese Academy of Sciences, Ser. B, Physical and Biological Sciences.