Stars orbiting the supermassive black hole at the middle of our Milky Way galaxy are mysteriously missing their binary companions, observations by the Keck Observatory in Hawaii have shown.
Stars often are available multiples. In our sun’s neighborhood, the fraction of binary star systems stands at 70%, meaning that out of each 100 stars, 70 exist in binary systems. For enormous stars this fraction is even higher, with just about all coming as binaries or triplets.
In the middle of our Milky Way galaxy, nonetheless, it’s a distinct story.
A team led by Devin Chu of the University of California, Los Angeles, analyzed 10 years’ price of observations tracking 28 stars orbiting our galaxy’s central supermassive black hole, which is generally known as Sagittarius A* and has a mass 4.1 million times that of the sun. The celebrities all orbit inside one light-month (480 billion miles, or 777 billion kilometers) of the black hole.
Sixteen of those so-called “S-stars” — named after the black hole — are very young (lower than six million years old) and are tens of times more massive than our sun.
“Stars this young shouldn’t even be near the black hole in the primary place,” said Chu in a statement (opens in recent tab). “They couldn’t have migrated to this region in only six million years, but to have a star form in such a hostile environment is surprising.”
Chu’s team was trying to find spectroscopic binaries. Sometimes, not even our greatest telescopes can resolve a binary system into two individual stars. In such cases, the one strategy to distinguish the components is by taking a look at their combined spectrum and observing a Doppler shift in the sunshine attributable to the celebs orbiting around each other.
Nonetheless, Chu’s team found that not one of the S-stars are binaries — all of them are singletons, confounding expectations that massive stars normally form in binary and even triplet systems. From their observations, Chu and his colleagues were capable of place an upper limit on the fraction of binaries around Sagittarius A* as being 47% at most, far lower than in our sun’s neighborhood.
“This difference speaks to the incredibly interesting environment of the middle of our galaxy; we’re not coping with a standard environment here,” said Chu.
Assuming that these massive stars did form as binaries, what became of their companions? One possibility is that the black hole’s mighty gravity was capable of split the binary systems, flinging considered one of the celebs out of the galaxy entirely. This hypothesis is supported by the population of so-called hypervelocity stars that astronomers have observed racing out of the galaxy at greater than 1 million mph (1.6 million kph).
One other possibility is that the black hole’s gravity disrupted the binary systems enough for pairs of stars to collide and merge. The merged star can be rejuvenated, appearing much younger than it truly is, which could help explain why stars that appear so young are present in an environment where it’s unlikely they may have formed.
“This … suggests that the black hole drives these nearby binary stars to merge or be disrupted, which has vital implications for the production of gravitational waves (opens in recent tab) and hypervelocity stars ejected from the galactic center,” said Chu. The following step, team members said, is to find out how the binary fraction changes with distance from Sagittarius A*.
The recent study (opens in recent tab) was published last week in The Astrophysical Journal.
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