In October 2017 astronomers experienced a premiere: for the first time, an object clearly originating from another star system could be observed during a guest performance in our solar system. Its discovery was somewhat lucky, as when it was discovered, the elongated asteroid Oumuamua was already on its way out.
Since then, the asteroid, dubbed the cigar, has captivated researchers and the public. A research team led by Coryn Bailer Jones of the Max Planck Institute for Astronomy has now traced the orbit of Oumuamua, identifying several star systems that may have been the original home of the “interstellar cigar”. None of these four stars, however, amounts to stellar prominence.
The star that Oumuamua came closest to just over a million years ago is the reddish dwarf star HIP 3757. Oumuamua’s orbit passed this star at a distance of less than two light-years. However, according to the researchers, the asteroid’s comparatively high relative speed (around 25 km / s) makes it unlikely that this is its origin. Another candidate, HD 292249, a sun-like star, would have seen the asteroid slightly less than 3.8 million years ago, but at a slower relative speed (10 km / s).
Oumuamua would have passed Candidates 3 and 4 1.1 and 6.3 million years ago respectively – with similar relative speeds and minimum distances. These last two stars are indeed in some surveys, but so far little is known about them. For the time being, therefore, they appear only under the numbers Gaia DR2 2502921019565490176 and Gaia DR2 3666992950762141312, named after the ESA astronomy satellite Gaia, on whose data the research team relied.
The data set Gaia Data Release 2 (DR2) contains precise information about 1.3 billion stars. For seven million stars, DR2 also provides information about the radial velocity of the star, that is, the portion of its motion that directs the star directly at us or away from us. With the help of the Simbad astronomical database, astronomers added another 220,000 stars to their study, whose radial velocity is contained in that database.
Next, astronomers considered a simplified scenario that assumes that both Oumuamua and all stars have been moving along straight lines and at constant speed over the last million years. From this scenario, they selected around 4,500 stars, which were promising candidates for a closer encounter with Oumuamua. These stars were then given a more accurate calculation and traced back to how Oumuamua and the stars in question moved.
However, the search is not completed yet: In 2021 more detailed data sets are to be published on several million stars, which could allow more accurate conclusions about the origin of the unusual asteroid.