In a groundbreaking study published in Proceedings of the Japan Academy, Series B, scientists have revealed that a star near the supermassive black hole at the center of the Milky Way galaxy has an extragalactic origin, marking the first time such a discovery has been made in the vicinity of a supermassive black hole.
Despite numerous stars being observed in proximity to the supermassive black hole Sagittarius A* at the galaxy’s center, the extreme gravitational forces make it inhospitable for stars to form in such an environment. Consequently, the stars observed near the black hole must have formed elsewhere and migrated towards it. This prompts the intriguing question: where did these stars originate?
Led by Shogo Nishiyama at Miyagi University of Education, an international team conducted research using the Subaru Telescope over an eight-year period to observe the star S0-6, positioned a mere 0.04 light-years away from Sagittarius A*. The findings indicate that S0-6, estimated to be around 10 billion years old, shares a chemical composition with stars found in smaller galaxies outside the Milky Way, such as the Small Magellanic Cloud and the Sagittarius dwarf galaxy.
The leading theory to explain S0-6’s composition suggests that it originated in a now-extinct small galaxy orbiting the Milky Way, ultimately being assimilated into our galaxy. This marks the first observational evidence supporting the idea that certain stars in the vicinity of Sagittarius A* were formed outside the Milky Way.
In its 10 billion years of existence, S0-6 would have traversed more than 50,000 light-years from its extragalactic birthplace to reach the proximity of Sagittarius A*. The journey likely involved a gradual spiral descent towards the galactic center rather than a direct trajectory.
While this discovery provides invaluable insights, questions persist. Nishiyama reflects on the ongoing mysteries, stating, “Did S0-6 truly originate beyond the Milky Way galaxy? Does it have any celestial companions, or did it traverse the vast cosmic expanse alone?” Further investigations are underway, offering the hope of unraveling the remaining enigmas surrounding stars near supermassive black holes.