The powerful gravitational forces, known as tidal forces, associated with the supermassive black hole (SMBH) at the center of our Galaxy are anticipated to inhibit the formation of stars close to it significantly. Stars located within a specific distance from the SMBH (1″) are thought to have formed at a greater distance from the black hole and then migrated to their current positions over time.
This raises the question, where did the stars form?
Research by an international team led by Shogo Nishiyama at Miyagi University of Education suggests that the star near the supermassive black hole at the center of the Milky Way galaxy originated outside of the Galaxy. The discovery marks the first instance where a star arising from outside our Galaxy has been identified in the proximity of a supermassive black hole.
The research led by Shogo Nishiyama at Miyagi University of Education, conducted by an international team, suggests that some stars may have originated from much farther away than previously believed—possibly from beyond the Milky Way.
Using the Subaru Telescope for eight years, the team observed the star S0-6, situated a mere 0.3 arcseconds from Sagittarius A*. Their findings reveal that S0-6 is over 10 billion years old and has a chemical composition resembling stars in smaller galaxies outside our Milky Way, like the Small Magellanic Cloud and the Sagittarius dwarf galaxy.
The leading theory explaining the makeup of S0-6 suggests that it originated in a small galaxy that no longer exists, which once orbited the Milky Way before being absorbed by it. This marks the first observational proof indicating that some stars close to Sagittarius A* were formed outside our Galaxy. Throughout its ten billion-year lifespan, S0-6 likely journeyed more than 50,000 light-years from beyond the Milky Way to reach the vicinity of Sagittarius A*. It is highly probable that S0-6 took a more circuitous route, gradually spiraling toward the center rather than taking a direct path.
Shogo Nishiyama at Miyagi University of Education said, “Did S0-6 really originate outside the Milky Way galaxy? Does it have any companions, or did it travel alone? With further investigation, we hope to unravel the mysteries of stars near the supermassive black hole.”
Journal Reference:
- Nishiyama et al. Origin of an Orbiting Star around the Galactic Supermassive Black Hole. Proceedings of the Japan Academy, Ser. B, Physical and Biological Sciences. DOI: 10.2183/pjab.100.007