A star near the supermassive black hole at the center of the Milky Way galaxy originated outside of the Galaxy according to a new study. This is the first time a star of extragalactic origin has been found in the vicinity of the super massive black hole.
Figure 1: The central region of the Milky Way galaxy as captured by the Subaru Telescope. The image shows many stars in a field of view about 3 arcseconds across. The star S0-6 (blue circle), the subject of this study, is located about 0.3 arcseconds from the supermassive black hole Sagittarius A* (Sgr A*, green circle). (Credit: Miyagi University of Education/ NAOJ)
Many stars are observed near the supermassive black hole known as Sagittarius A* at the center of our Galaxy. But the black hole’s intense gravity makes the surrounding environment too harsh for stars to form near the black hole. All the observed stars must have formed somewhere else and migrated towards the black hole. This raises the question, where did the stars form.
Research by an international team led by Shogo Nishiyama at Miyagi University of Education indicates the some of the stars may have come from farther away than previously thought, from completely outside of the Milky Way. The team used the Subaru Telescope over the course of eight years to observe the star S0-6 located only 0.3 arcseconds away from Sagittarius A*. They determined that S0-6 is more than 10 billion years old and has a chemical composition similar to stars found in small galaxies outside the Milky Way, such as the Small Magellanic Cloud and the Sagittarius dwarf galaxy.
The most likely theory to explain the composition of S0-6 is that it was born in a now extinct small galaxy orbiting the Milky Way that was absorbed. This is the first observational evidence suggesting that some of the stars in the vicinity of Sagittaius A* formed outside of the Galaxy. Over its 10 billion year life, S0-6 must have travelled more than 50,000 light-years from outside of the Milky Way to reach the vicinity of Sagittarius A*. Almost certainly S0-6 traveled much more than 50,000 light-years, slowly spiraling down to the center rather than making a straight shot.
There are still many questions according to Nishiyama, "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."
These results appeared as Nishiyama et al. "Origin of an Orbiting Star around the Galactic Supermassive Black Hole" in the online edition of "Proceedings of the Japan Academy, Ser. B, Physical and Biological Sciences" on December 1, 2023.
This research was conducted by a team of researchers from Miyagi University of Education, Daido University, Wakayama National College of Technology, Aichi University of Education, Tohoku University, Waseda University, National Astronomical Observatory of Japan, Observatoire de la Côte d’Azur, and Instituto de Astrofísica de Andalucía.
This research is supported by the following Grants-in-Aid for Scientific Research: Grant-in-Aid for Scientific Research (A), 18H03720, 19H00695, 20H00178; Grant-in-Aid for Scientific Research (B), 19H01900; Grant-in-Aid for Challenging Exploratory Research, 18K18760; Grant-in-Aid for Challenging Budding Researchers, 15K13463. S. Nishiyama is supported by the Tohoku Initiative for Fostering Global Researchers for Interdisciplinary Sciences (TI-FRIS), a project of the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).
The Subaru Telescope is a large optical-infrared telescope operated by the National Astronomical Observatory of Japan, National Institutes of Natural Sciences with the support of the MEXT Project to Promote Large Scientific Frontiers. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawai`i.
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