‘Oumuamua’, the rocky object identified as the first confirmed interstellar asteroid, very likely came from a binary star system, a study has found. “It’s remarkable that we have now seen for the first time a physical object from outside our solar system,” said Alan Jackson from the University of Toronto Scarborough in Canada.
A binary star system, unlike our Sun, is one with two stars orbiting a common centre. For the study, published in the journal Monthly Notices of the Royal Astronomical Society, Jackson and colleagues tested how efficient binary star systems are at ejecting objects. They also looked at how common these star systems are in our galaxy. The researchers found that rocky objects like ‘Oumuamua’ are far more likely to come from binary than single star systems. They were also able to determine that rocky objects are ejected from binary systems in comparable numbers to icy objects.
“It’s really odd that the first object we would see from outside our system would be an asteroid, because a comet would be a lot easier to spot and the Solar System ejects many more comets than asteroids,” said Jackson. Once the researchers determined that binary systems are very efficient at ejecting rocky objects, and that a sufficient number of them exist, they were satisfied that ‘Oumuamua’ very likely came from a binary system. They also concluded that it probably came from a system with a relatively hot, high mass star since such a system would have a greater number of rocky objects closer in.
The team suggests that the asteroid was very likely to have been ejected from its binary system sometime during the formation of planets. ‘Oumuamua’, which is Hawaiian for ‘scout’, was first spotted by the Haleakala Observatory in Hawaii in October last year. With a radius of 200 metres and travelling at a blistering speed of 30 kilometres per second, at its closest it was about 33,000,000 km from Earth.
When it was first discovered researchers initially assumed the object was a comet, one of countless icy objects that release gas when they warm up on approaching the Sun. However, it did not show any comet-like activity as it neared the Sun, and was quickly reclassified as an asteroid, meaning it was rocky. Researchers were also fairly sure it was from outside our solar system, based on its trajectory and speed.