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In an article published in the Letters from the Astrophysical Journal, Harvard University astrophysicists Avi Loeb and Amir Siraj show that a stellar companion of mass equal to the Sun in the solar birth cluster – the collection of stars that formed with our star from the same dense cloud of molecular gas – at a separation of 1000 DU would have increased the probability of forming the population of objects observed in the outside Oort Cloud and capture the planet nine hypothesis.
An artist’s conception of a potential solar companion, which theorists say was developed in the Sun’s birth cluster and later lost. If proven, the solar companion theory would give additional credibility to the theories that the Oort cloud formed as we see it today, and that planet nine was captured rather than formed in place. Image credit: M. Weiss.
Popular theory associates the formation of the Oort cloud with debris left over from the formation of the solar system and its neighbors, where objects were scattered by planets at great distances and some were swapped between stars.
But a binary model could be the missing piece of the puzzle and should come as no surprise to scientists.
“Previous models struggled to produce the expected ratio between scattered disk objects and external Oort Cloud objects,” said Siraj, an undergraduate student in the Department of Astronomy at Harvard University.
“The binary capture model offers significant improvement and refinement, which is apparently evident in retrospect: most Sun-like stars are born with binary companions.”
If the Oort Cloud were indeed captured with the help of one of the first stellar companions, the implications for our understanding of the formation of the solar system would be significant.
“Binary systems are much more efficient at capturing objects than single stars,” Professor Loeb said.
“If the Oort cloud formed as observed, it would imply that the Sun actually had a similar mass companion that was lost before the Sun left its birth cluster.
More than a simple redefinition of how our solar system was formed, evidence from a captured Oort cloud could answer questions about the origins of life on Earth.
“Objects in the outer Oort cloud may have played an important role in Earth’s history, such as bringing water to Earth and causing the dinosaurs to become extinct. It’s important to understand their origins, ”Siraj said.
The model also has implications for the planet nine hypothesis, which the team says is not the only one.
“The puzzle is not just about the Oort clouds, but also extreme trans-Neptunian objects, like the potential New Planet,” Professor Loeb said.
“We don’t know where they came from, and our new model predicts that there should be more objects with similar orbital orientation to planet nine.”
If the Sun had an early companion who helped form the outer solar system, its current absence begs the question: where has it gone?
“Passing stars through the birth cluster would have moved the companion away from the Sun thanks to their gravitational influence,” Professor Loeb said.
“Before the loss of the binary, however, the solar system would have already captured its outer shell of objects, namely the Oort cloud and the population of planet nine,” Siraj added.
“The Sun’s long-lost companion could now be found anywhere in the Milky Way.”
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Amir Siraj and Abraham Loeb. 2020. The case of a first solar binary companion. ApJL 899, L24; doi: 10.3847 / 2041-8213 / abac66
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