Observations by the Keck Observatory in Hawaii have shown that stars orbiting the supermassive black hole at the center of our Milky Way galaxy are mysteriously missing their binary companions.
Stars often come with multiples. In the vicinity of our sun, part of binary star systems It stands at 70%, which means that out of every 100 stars, 70 are in binary systems. For massive stars, this part is even higher, as almost all of them come as doubles or triplets.
in the middle milky way The galaxy, however, is a different story.
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A team led by Devin Chu of the University of California, Los Angeles, analyzed 10 years of observations tracking 28 stars orbiting the center of our galaxy. Giant black holewhich is known as arch a* Its mass is 4.1 million times that of the Sun. All stars orbit within one light-month (480 billion miles, or 777 billion km) from Black hole.
Sixteen of these so-called “S-stars” – named after the black hole – are very young (less than six million years old) and are tens of times more massive than our Sun.
Zhou said in a statement (Opens in a new tab). “Not only could they have migrated to this region in six million years, but for them to have a star shape in such a hostile environment is amazing.”
Chu’s team was looking for spectral binaries. Sometimes even our best telescopes can’t resolve a binary system into two individual stars. In such cases, the only way to distinguish the components is to look at their combined spectrum and observe the Doppler shift in the light caused by the stars orbiting each other.
However, Chu’s team found that none of the S stars are binary — they are all singletons, confounding predictions that massive stars usually form in binary or even triple systems. From their observations, Zhu and his colleagues were able to place an upper limit on the fraction of binaries around Sagittarius A* as being 47% at most, which is much lower than in our solar vicinity.
“This difference speaks to the incredibly interesting environment of our galaxy’s center; we’re not dealing with a normal environment here,” Zhou said.
Assuming that these massive stars formed as binaries, what happened to their companions? One possibility is that the black hole’s massive gravity was able to split binary systems apart, kicking one of the stars out of the galaxy entirely. This hypothesis is supported by so-called hypervelocity stars that astronomers have observed racing out of the galaxy at more than a million miles per hour (1.6 million kilometers per hour).
Another possibility is that the black hole’s gravity disrupted the binary systems enough for pairs of stars to collide and merge. The merged star will regenerate, appearing much younger than it really is, which may help explain why stars that appear so young are in an environment in which they are unlikely to have formed.
“This … indicates that the black hole is driving these nearby binary stars to merge or disrupt, which has important implications for the production of gravitational waves (Opens in a new tab) and hypervelocity stars emerging from the center of the galaxy,” Zhou said. The next step, team members said, is to see how the binary fraction changes with distance from Sagittarius A*.
the New study (Opens in a new tab) It was published last week in The Astrophysical Journal.
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