Using data from ESA’s Gaia stellar surveyor, astronomers have identified four stars that are possible places of origin of ‘Oumuamua, an interstellar object spotted during a brief visit to our Solar System in 2017.

The discovery last year sparked a large observational campaign: originally identified as the first known interstellar asteroid, the small body was later revealed to be a comet, as further observations showed it was not slowing down as fast as it should have under gravity alone. The most likely explanation of the tiny variations recorded in its trajectory was that they are caused by gasses emanating from its surface, making it more akin to a comet.

But where in the Milky Way did this cosmic traveller come from?

Comets are leftovers of the formation of planetary systems, and it is possible that ‘Oumuamua was ejected from its home star’s realm while planets were still taking shape there. To look for its home, astronomers had to trace back in time not only the trajectory of the interstellar comet, but also of a selection of stars that might have crossed paths with this object in the past few million years.

“Gaia is a powerful time machine for these types of studies, as it provides not only star positions but also their motions,” explains Timo Prusti, Gaia project scientist at ESA.

To this aim, a team of astronomers led by Coryn Bailer-Jones at the Max Planck Institute for Astronomy in Heidelberg, Germany, dived into the data from Gaia’s second release, which was made public in April.