Did a Star Venture Across 50,000 Light-Years to Reach the Milky Way?

Saturday - December 9 2023, 17:16 UTC - 11 months ago

The Subaru Telescope has observed a star, designated "S0-6," which has likely ventured from a far away galaxy over a period of 10 billion years, before arriving at the vicinity of the supermassive black hole of the Milky Way. The star was found to be located 0.4 light-years away from the black hole, and its chemical composition was similar to that of stars measured in nearby galaxies of the Milky Way. The findings were reported in the journal Proceedings of the Japan Academy, Series B.

The central region of our Milky Way galaxy is a tumultuous and extreme environment, mainly due to the presence of a supermassive black hole dubbed Sagittarius A*. This black hole's enormous gravitational forces generate a wildly chaotic environment, making it difficult for stars to develop in its proximity. Despite these harsh conditions, astronomers believe that certain stars still exist in the neighborhood of the black hole. But there's a catch: these stars didn't develop here but rather traveled immense cosmic distances to end up here, unable to escape the black hole's tremendous gravity.

The Subaru Telescope has closely studied one such star, designated "S0-6," for nearly eight years. The researchers at Miyagi University of Education, who conducted the observations, believe the invader star may have traveled 50,000 light-years to its current location. According to the official press release, this is the first time an extragalactic star has been observed hanging near a supermassive black hole.

Distance between the star and black hole .

The 8.2-meter Subaru Telescope, located on the summit of Maunakea, Hawai'i, collected extensive data on several features of this star. This contained data on its velocity and trajectory, as well as information on the light it emits and its chemical composition. As per the official release, this rogue star was found to be located only 0.3 arcseconds away from Sagittarius A* —- merely 0.04 light-years away. In astronomy, an arcsecond is a unit of angular measurement commonly used to express small angles.

The spectrum data indicated that this star has a low concentration of heavy elements and is most likely more than 10 billion years old. S0-6 has a chemical makeup similar to stars seen in nearby galaxies of 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 Sagittarius A* formed outside of the Galaxy," noted the release.

This star may have gradually spiraled across vast distances of space throughout its ten billion-year existence, finally arriving in the vicinity of Sagittarius A*.

The authors highlight that this comprehensive observation has raised a few questions, including "Did S0-6 really originate outside the Milky Way galaxy? Does it have any companions, or did it travel alone?" .

The team now intends to undertake further observations to find answers to these key questions.

The findings were reported in the journal Proceedings of the Japan Academy, Series B.

Study abstract: .

The tremendous tidal force that is linked to the supermassive black hole (SMBH) at the center of our galaxy is expected to strongly subdue star formation in its vicinity. Stars within 1" from the SMBH thus likely formed further from the SMBH and migrated to their current positions. In this study, spectroscopic observations of the star S0-6/S10, one of the closest (proj. 0.3") star to the SMBH were undertaken with the 8.2m Subaru Telescope. We derived the star's radial velocity and Internal velocity dispersion, as well as its abundances of several key elements (C, N, O, Na, Mg, Al, Si, K, Ca), which we find to be comparable to those of stars measured in Local Group dwarf galaxies. Our results strongly indicate that S0-6 formed in the early universe, a time when dwarf galaxies in the halo of the Milky Way had yet to be formed.