Scientists at the Max Planck Institute for Astronomy have identified four potential candidates for the home of 'Oumuamua, the first interstellar object known to visit the solar system. Based on data from ESA's Gaia stellar surveyor satellite, the four stars match the back-projected trajectory of 'Oumuamua, showing it came within two light years of each of them between one and seven million years ago.
When 'Oumuamua passed through the solar system in 2017, it was an astronomical sensation that prompted a flurry of activity. Space scientists raced to track its orbit and learn more about its property as it shot past on a hyperbolic course into and back out of the solar system.
Over a year later, 'Oumuamua has given up some of its secrets. First suspected as being an asteroid, the shifts recorded in its trajectory suggest that it was shooting out gas jets as it approached the Sun, indicating that its more of a comet – though one so coated with organic molecules that it's a very asteroid-like comet. In addition, scientists now suspect that 'Oumuamua came from a star very similar to our own, though very likely part of a binary system with a large companion that hurled it into interstellar space millions of years ago.
Researchers have also worked on back tracking 'Oumuamua's trajectory to find out where exactly its home is, but the Milky Way is a very big place with a lot of stars, and calculating its galactic orbit has proven very complex.
To narrow the search down, the Planck Institute team led by Coryn Bailer-Jones looked for stars that might have once crossed 'Oumuamua's path. Data released in April by ESA from the Gaia satellite proved a valuable tool for this task because it doesn't just map stars by their position, it also records their radial velocity or how they are moving in relation to the Earth.
This data allowed the team to narrow down an initial set of seven million stars, plus another 220,000 others from the astronomical literature, to just four that 'Oumuamua came close enough to for one of them to be its home. Equally important, each of these stars had a low enough relative velocity that 'Oumuamua could have been ejected from their orbit.
The four stars are all dwarfs of a size equal to or smaller than the Sun, but none is known to be a binary or to have a massive, dark companion like a giant planet or a brown dwarf. Future observations might help to either narrow down (or expand) the candidate list as more data from Gaia is released in the years to come.
"While it's still early to pinpoint 'Oumuamua's home star, this result illustrates the power of Gaia to delve into the history of our Milky Way galaxy," says Timo Prusti, Gaia project scientist at ESA.
The research was published in The Astronomical Journal.
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