There is no trace of binary stars in the center of the Milky Way

Search table of stars included in the periodicity search. – THE ASTROPHYSICAL JOURNAL (2023). DOI: 10.3847/153

The stars that live closest to the supermassive black hole at the center of the Milky Way have no stellar companions, according to observations with the W.M. Keck, in Hawaii.

Devin S. Chu, an astronomer with the Galactic Center Orbits Initiative at UCLA (University of California Los Angeles), led a 10-year study that found that these “S stars” – where “S” stands for Sagittarius A star, the name of the monstrous black hole in the center of our galaxy – are all single.

The result is surprising given that the S stars Chu’s team observed included young, massive main-sequence stars that are only about six million years old. Typically, stars of this age that are 10 times more massive than our Sun spend their childhood years paired with a twin in a binary system, or sometimes even as triplets.

“This discovery speaks to the incredibly interesting environment of the Galactic Center,” said Chu, lead author of the study published in The Astrophysical Journal. “The powerful influence of the supermassive black hole is likely to cause binary star systems to merge or break apart. This may explain why we don’t see stars with such close partners to the Sagittarius A star.”

Using the Keck Observatory’s adaptive optics system in conjunction with its OH-suppressing infrared imaging (OSIRIS) spectrograph, Chu and his team tracked the movements of 28 S stars; 16 of which are young B-type main sequence stars and the rest are old low-mass M- and K-type giant stars. “Keck’s adaptive optics and OSIRIS have been crucial in providing us with the infrared information we needed to peer through the dust of the Galactic Center and distinguish individual S stars in this highly populated region,” Chu said in a statement.

Not only did they find the S stars flying by themselves, the researchers were also able to calculate the limit of how many of these S stars could exist as binaries, a metric known as a binary fraction. They found that the binary fraction cutoff for young S stars is 47 percent, which means that for every 100 S stars, a maximum of 47 of them could be in binary systems. This limit is dramatically lower than expected for similar types of young stars in Earth’s solar neighborhood, which have a binary fraction of 70 percent. The finding suggests that stars with companions have a hard time sticking together in the extreme environment of the Milky Way’s supermassive black hole.

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