"Around about 10 billion years ago the Milky Way collided with a small sausage-shaped galaxy in a titanic event that determined the futures of both."

https://cosmosmagazine.com/space/a-g...-the-milky-way

In a series of five papers published in the journals Monthly Notices of the Royal Astronomical Society and The Astrophysical Journal Letters, as well as the preprint site arXiv.org, astronomers from the Simons Foundation Centre for Computational Astrophysics in the US lay out evidence that suggests the shape and size of our home galaxy was substantially affected by a violent encounter with a dwarf one they dub “The Sausage”.

“The collision ripped the dwarf to shreds, leaving its stars moving in very radial orbits,” explains one of the researchers, Vasily Belokurov.

The stars, freed from the gravitational forces of their own galaxy, continued speeding along, following trajectories that took them very close to the centre of the Milky Way. Their journey, adds Belokurov, “is a telltale sign that the dwarf galaxy came in on a really eccentric orbit and its fate was sealed”.