ESA's Gaia Spots Stars Flying Between Galaxies

A team of astronomers using European Space Agency's (ESA) Gaia telescope to look for signs of distant stars being kicked out of the Milky Way galaxy instead found stars heading inwards perhaps from another galaxy.

The discovery, led by a team from the Leiden University in the Netherlands, found 20 stars going so fast they expect them to escape our galaxy.

Out of these, seven stars were moving away from the Galaxy and 13 were racing towards the Milky Way, the astronomers said.

"Of the seven million Gaia stars with full 3D velocity measurements, we found twenty that could be travelling fast enough to eventually escape from the Milky Way," said Elena Maria Rossi, from the varsity.

However, "rather than flying away from the Galactic centre, most of the high-velocity stars we spotted seem to be racing towards it," added co-author Tommaso Marchetti from the varsity.

"These could be stars from another galaxy, zooming right through the Milky Way," Marchetti said.

Stars circle around our galaxy at hundreds of kilometres per second, and their motions contain a wealth of information about the past history of the Galaxy.

The fastest class of these stars are called hypervelocity stars, which are thought to start their life near the Galactic centre, later to be flung towards the edge of the Milky Way via interactions with the black hole at its centre.

Another explanation could be that the newly identified sprinting stars could be native to our Galaxy's halo, accelerated and pushed inwards through interactions with one of the dwarf galaxies that fell towards the Milky Way during its build-up history, the astronomers explained.

The new data, published in the journal Monthly Notices of the Royal Astronomical Society, will help to nail down the nature and origin of these stars with more certainty, and the team will use ground-based telescopes to find out more about them.