Remember that 'weird' interstellar comet? Astronomers have narrowed down its home star system

Astronomers are getting closer to determining where a strange visitor from another stellar system came from.

4 stars could be home to strange, cigar-shaped comet from another star system

An artist's illustration of the interstellar object 'Oumuamua, which appears to be outgassing material. It was discovered by Canadian astronomer Robert Weryk last fall. (ESA/Hubble, NASA, ESO, M. Kornmesser)

It was a surprise visitor that astronomers believe travelled for billions of years before whizzing through our solar system. Astronomers had no idea where this "weird" interstellar interloper came from, but scientists have now narrowed its origins to just four stars — out of 1.6 billion.

'Oumuamua is a strangely shaped rock discovered last October by Canadian astronomer Robert Weryk, at the University of Hawaii's Institute for Astronomy.

The story of 'Oumuamua is an intriguing one, as there was debate over whether it was a comet or an asteroid. (Researchers eventually determined it was a comet.) 

It is also the first known interstellar visitor, and, as a result, astronomers are keen to understand how and why it was ejected from its star system — something that would require a unique set of circumstances.

A diagram that shows the trajectory and location of 'Oumuamua on Dec. 12, 2017. (NASA/JPL)

"It is a very interesting object that immediately raises the question: Where does it come from?" said Timo Prusti, Gaia project scientist at the European Space Agency. "People have been trying to address this issue with existing data right from the beginning when it was discovered. But the quality of the available data wasn't good enough to really find any candidates."

Enter the ESA's space telescope, Gaia, which has been in orbit since 2013.

Gaia has the unique job of mapping our galaxy in 3D, and one of its attributes is that it is able to calculate the movement and velocity of the stars in our galaxy.

Using the first 22 months of data from the Gaia mission, an international group of scientists narrowed down 'Oumuamua's home to four small dwarf stars: HD 292249, HIP 3757 and two others without names.

The paper has been approved for publication in the Astronomical Journal, but is currently available on

The current theory is that 'Oumuamua was ejected from a binary — or two-star — system during its star's planet-formation stage. It's not yet known whether any of these four stars are binary systems.

Potentially more candidates

And while 1.6 billion stars sounds like a lot, it's really just a drop in the bucket.

"It sounds like a huge number," Prusti said. "But we always have to remind ourselves that in our Milky Way, that it represents only one per cent of the stars."

While there's only been 22 months of data analyzed so far, another batch of data, encompassing 34 months, will be released in 2021. But if you think that will help narrow things down further for 'Oumuamua, it's not that simple: The new data will add millions more stars that could produce new candidates for the comet's home system.

An all-sky view of our Milky Way and neighbouring galaxies, based on measurements of nearly 1.7 billion stars. The map shows the density of stars, observed by the Gaia space telescope, in each portion of the sky between July 2014 to May 2016. ​The two bright objects in the lower right are the Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way. (Gaia Data Processing and Analysis Consortium (DPAC); A. Moitinho/A. F. Silva/M. Barros, et al.)

According to Prusti, that might not be a bad thing.

"What might be is that among the stars, we might get a better candidate, where the velocities — and also how close the encounter — are a better match than for these four stars," he said. "It might be that we get many more candidates, but one or two of them are really good candidates."

So far, Gaia has proved to be invaluable to astronomers trying to learn more about our galaxy, which, in turn, helps them test theories and better understand the universe.

Last week, a study using Gaia data revealed that the stars in our galaxy are still dealing with the effects of a galactic near-collision that occurred somewhere between 300 and 900 million years ago.


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