Astronomers have discovered fast-moving wandering stars that appear to be invading our galaxy, the Milky Way.
The team was studying data from the European Space Agency’s Gaia space telescope looking for evidence of “high velocity” stars.
To their surprise they found a group of stars spiralling towards the galactic centre instead of away from it, as expected.
The most likely explanation is that they originated outside the Milky Way in another galaxy.
Dr Tommaso Marchetti, one of the astronomers from Leiden University in the Netherlands, said: “Rather than flying away from the Galactic centre, most of the high-velocity stars we spotted seem to be racing towards it.
“These could be stars from another galaxy, zooming right through the Milky Way.”
Stars including the sun whirl around the centre of the galaxy at hundreds of kilometres per second.
The fastest moving high-velocity stars are thought to start their life near the galactic centre before being flung towards the edge of the Milky Way.
The Gaia scientists discovered 20 that looked as if they were travelling fast enough to escape from the galaxy, but most of them were moving inwards, not outwards.
The stars may have come from the Large Megellanic Cloud, a small galaxy orbiting the Milky Way, the astronomers believe. Or they may have journeyed from somewhere even further away.
Study co-author Dr Elena Maria Rossi, also from Leiden University, said: “Stars can be accelerated to high velocities when they interact with a supermassive black hole.
“So the presence of these stars might be a sign of such black holes in nearby galaxies. But the stars may also have once been part of a binary system, flung towards the Milky Way when their companion star exploded as a supernova.
“Either way, studying them could tell us more about these kinds of processes in nearby galaxies.”
The research appears in the journal Monthly Notices of the Royal Astronomical Society.