'Oumuamua: Scientists May Have Found Where Mysterious Interstellar Comet Came From

An artist's impression of 'Oumuamua. ESA/Hubble, NASA, ESO, M. Kornmesser

Astronomers have identified four stars as candidates for the place where a mysterious interstellar object known as 'Oumuamua may have originated.

The roughly 800- by 100-foot object, shaped like a cigar, was first discovered in October 2017, hurtling through space at speeds of around 16 miles per second. Unlike anything that had ever been seen before, it was identified as the first known interstellar visitor to our solar system and classified as an asteroid, although subsequent analysis led to it being named a comet.

Despite these findings, the object's origins remain a mystery. But now, using the second release of data collected by the European Space Agency's Gaia space observatory, researchers think they may have zeroed in on a handful of potential home stars.

Comets are remnants of the formation of planetary systems, so it's possible that 'Oumuamua—which roughly translates to scout or messenger in the Hawaiian language—was ejected from its home star during this phase.

To narrow down where 'Oumuamua, came from, a team led by Coryn Bailer-Jones of the Max Planck Institute for Astronomy in Heidelberg, Germany, traced the object's trajectory back in time, as well as a selection of stars that it could conceivably have crossed paths with in the past few million years.

The Gaia data was particularly helpful, in this case, because it contains information about the positions, distance indicators and motions for more than a billion stars in our galaxy. And most important, it also includes the radial velocities—how fast they are moving away or toward Earth—for a set of 7 million stars.

Within this group of 7 million, the team identified four stars whose orbits had taken them within two light-years of 'Oumuamua in the relatively recent past—between 1 million and 7 million years ago—and which also had radial velocities that were low enough to be consistent with plausible ejection trajectories. The results have been accepted for publication in The Astronomical Journal.

"We have identified four stars which are plausible origin stars for 'Oumuamua, in the sense that the stars came close to 'Oumuamua in the past at a relatively low speed," Bailer-Jones told Newsweek.

The potential homes are all dwarf stars with masses similar to, or smaller than, our sun's. However, while they are plausible candidates, none are known to host large planets or have a companion "binary" star. Scientists think that one of these would need to be present to eject the small body from the system.

Nevertheless, future observations of these four star systems may reveal as yet unknown characteristics that could boost their chances of being 'Oumuamua's home. Furthermore, planned releases of Gaia data—which are due in the early 2020s—will include radial velocities for many more stars, which might lead to the identification of additional candidates.

Alan Jackson, an astronomer and planetary scientist from the University of Toronto, who was not involved in the latetest research, described the study as "very well done," while noting that we should still be cautious about the evidence provided.

"It is precisely the sort of thing that really allows the superb quality of the data provided by the Gaia satellite to shine," he told Newsweek. "As the authors themselves say though, none of the four candidates they identify are really an obvious smoking gun for the origin of 'Oumuamua."

"The closest encounter they identify is at a distance of almost two light-years," he said. "For comparison, the outer edge of our own Oort cloud of comets is typically thought to be about one light-year, and ejections usually occur through interactions with the planets that lie very much closer."

This article has been updated to include additional comments from Alan Jackson.