Cosmic collision with 'Sausage' galaxy reshaped Milky Way

Astronomers have discovered an ancient cosmic collision with an object, dubbed the "Sausage" galaxy, that reshaped the structure of the Milky Way galaxy.

The crash was a defining event in the early history of the Milky Way and helped fashion both its inner bulge and its outer halo, according to a series of studies published in the Monthly Notices of the Royal Astronomical Society and The Astrophysical Journal Letters.

Scientists propose that around 8 billion to 10 billion years ago, an unknown dwarf galaxy smashed into our own Milky Way. The dwarf did not survive the impact: It quickly fell apart, and the wreckage is now all around us.

"The collision ripped the dwarf to shreds, leaving its stars moving in very radial orbits" that are long and narrow like needles, said Vasily Belokurov of the University of Cambridge in the UK.

The stars' paths take them "very close to the centre of our galaxy. This is a telltale sign that the dwarf galaxy came in on a really eccentric orbit and its fate was sealed."
Sausage debris was scattered all around the inner parts of the Milky Way, creating the 'bulge' at the galaxy's centre and the surrounding 'stellar halo.'